Promising (1861) (epaggello) pictures these deceivers as announcing proclamations with a sense of certainty that the promise will be fulfilled. The false teachers never cease proclaiming (present tense indicates continuous action -- lie, lie, lie - that was their modus operandi!) their deceitful promise of "freedom" but as shown below their walk does not match their talk. Peter uses a bit of sarcasm here emphasizing the ridiculousness of the possibility that people who are slaves of sin themselves could ever set anybody else free! 

Be careful when someone promises you freedom with "no strings attached" (e.g., freedom to live as you please), because true spiritual freedom in Christ is not the right to do as you please, but is the liberty (and the power) to do as you should. No man is right to do as he pleases unless he pleases to do right! In other words, true Christian liberty is the liberty from sin and not to sin. The glory of the Gospel brings spiritual freedom, while the disgrace of this "brand" of false teaching brings bondage to sin, self and Satan.

In his first letter Peter wrote that believers are to...

Act as free men, and do not use your freedom as a covering for evil, but use it as bondslaves of God. (See note 1Pe 2:16)

Jonathan Edwards said it this way...

True liberty consists only in the power of doing what we ought to will, and in not being constrained to do what we ought not to will.

Oswald Chambers phrased it this way...

Liberty means ability not to violate the law of God. License means personal insistence on doing what I like.

A W Tozer put it in pithy terms writing that...

The important thing about a man is not where he goes when he is compelled to go, but where he goes when he is free to go where he will...Where we go when we are free to go where we will is a near-infallible index of character.

Freedom (1657)  (eleutheria from eleutheros - that which is capable of movement, freedom to go wherever one likes, unfettered; see word study on verb eleutheroo) describes the state of being free and stands in opposition to slavery or bondage.

Vine writes that it means...

“liberty” , is rendered “freedom” in Gal. 5:1, “with freedom did Christ set us free.” The combination of the noun with the verb stresses the completeness of the act, the aorist (or point) tense indicating both its momentary and comprehensive character; it was done once for all. The RV margin “for freedom” gives perhaps the preferable meaning, i.e., “not to bring us into another form of bondage did Christ liberate us from that in which we were born, but in order to make us free from bondage.”

The word is twice rendered “freedom” in the RV of Gal. 5:13 (KJV, “liberty”). The phraseology is that of manumission from slavery, which among the Greeks was effected by a legal fiction, according to which the manumitted slave was purchased by a god; as the slave could not provide the money, the master paid it into the temple treasury in the presence of the slave, a document being drawn up containing the words “for freedom.” No one could enslave him again, as he was the property of the god. Hence the word apeleutheros, No. 2. The word is also translated “freedom” in 1 Pet. 2:16, rv. In 2 Cor. 3:17 the word denotes “freedom” of access to the presence of God. See liberty. (Vine, W E: Vine's Complete Expository Dictionary of Old and New Testament Words. 1996. Nelson)

Eleutheria refers to personal liberty but not license. The deceiving (and deceived - see 2Ti 3:13-note) false teacher promise their listeners the freedom to live as they please. To the contrary, true liberty is living as we should not as we please. Eleutheria was used especially in NT times of the freeing of slaves.

NIDNTT writes that in classic Greek...

The noun eleutheria is derived from the adjective eleutheros. O. Schrader derives it from the Indo-Germanic *leudh-, belonging to the people, and thus not subject. It is connected with Lat. liber (free), and Schrader links it with Old High German liut, Modern German Leute, people (Reallexikon der indogermanischen Altertumskunde, II 19292, 454 f.; but cf. Liddell-Scott, 532). In so far as a man belongs to the people, he is a free citizen as contrasted with a slave or foreigner. Eleutheria thus means freedom, independence, in the sense of being independent of others, being able to dispose. This way of speaking arose originally in contrast to the bondage of slaves. Similarly, the adjective eleutheros means free, not bound, of free birth. It also indicates someone who is his own master. Later the noun and the adj. could occasionally be used to denote the mental attitude which makes use of freedom. It could be used (as it mostly was) in the good sense of noble, being in control of oneself, magnanimous, generous. But it could also be used in the less frequent and bad sense of being reckless, or unrestrained.

In secular Gk. eleutheros has primarily a political sense. The eleutheros is the full citizen who belongs to the polis, the city state, in contrast to the slave who did not enjoy full rights as a citizen. Freedom consists in his right to participate fully in public debates over civic matters. It is the right of free speech, parrhesia openness, boldness, frankness. He can decide about his own affairs within the polis. On numerous occasions, Aristotle spoke of the Gk. polis as the community of the free. He considered freedom to be the essential good of the polis. But in order to preserve this freedom, the law (nomos) is required as the principle of order. Freedom and law are thus not contradictory opposites. They belong together and qualify each other. The constant danger is rejection of the law in the name of a misconceived freedom which is purely arbitrary, because it is willing to grant itself more freedom than it is willing to grant to others. This idea of freedom was naturally applied to relations between states which gave rise to the idea of sovereignty. (See further H. Schlier, TDNT II 487-92.)

The mystery religions had their own answer to the question of freedom. Through the cultic rites, the initiate was freed from this hopeless world and obtained a part in the destiny of the deity

In the most basic form, this word group related to a "free man" in contrast with a slave. Such persons were usually born free, but some of them had purchased their freedom.

There are 17 uses of eleutheria in the NT...

Romans 8:21 (note) that the creation itself also will be set free from its slavery to corruption into the freedom of the glory of the children of God.

Comment: Freedom in this context refers to the time when all believers will be liberated finally and completely from the effects and temptation of fallen flesh nature and set free even from the pleasure of sin, to share eternally in God’s glory, with which He will clothe all His liberated sons and daughters.

1 Corinthians 10:29 I mean not your own conscience, but the other man's; for why is my freedom judged by another's conscience?

Comment:  Freedom is presented as the supreme blessing of the new covenant of grace, which, in contrast with the Old covenant of law, is represented as including independence from religious regulations and legal restrictions (1Co 10:29; 2Co 3:17; Ga 2:4; 2Pe 2:19).

John MacArthur writes

Our own freedom should not be judged by another’s conscience. That is, we should not cause our freedom to be slandered by expressing it in ways that offend a weaker brother. We should give thanks for the food and for our liberty and then express our liberty by choosing not to eat the food that offends the brother. How can we be thankful to the Lord for something a Christian brother or sister is going to stumble over?

A T Robertson comments that

Paul deftly puts himself in the place of the strong brother at such a banquet who is expected to conform his conscience to that of the weak brother who makes the point about a particular piece of meat. It is an abridgment of one’s personal liberty in the interest of the weak brother. Two individualities clash. The only reason is love which builds up (1Co 8:2 and all of 1Cor 13:1ff). There is this eternal collision between the forces of progress and reaction. If they work together, they must consider the welfare of each other.

2 Corinthians 3:17 Now the Lord is the Spirit; and where the Spirit of the Lord is, there is liberty.

Comment: In context believers now have freedom of access to God without fear in opposition to the fear in Ex. 34:30. We need no veil and we have free access to God. The end of the dominance of the Law means liberty.

Galatians 2:4 But it was because of the false brethren who had sneaked in to spy out our liberty which we have in Christ Jesus, in order to bring us into bondage (to the law, legalism).

Comment: Here eleutheria describes the unfettered condition of the Christian soul in contrast with the Jewish condition of bondage to law. Spiritual liberty or spiritual bondage? Note the Source of the freedom is "in Christ Jesus", made effective by the Spirit of Christ who indwells believers - see 2Co 3:17. Christian freedom is not license. When we become free in Christ we lose our freedom to sin, of which we were once a slave.

Galatians 5:1  It was for freedom that Christ set us free; therefore keep standing firm and do not be subject again to a yoke of slavery.

Comment: Human freedom that in which man was originally created, is not liberty to do wrong or to indulge oneself, but in fact is liberty to obey God. As Vine says "Man is so constituted that only as he pleases God can he be happy in the higher, the spiritual, part of his nature, and efficient for the great ends for which he was created. The essence of the Fall lay in this, that man used his endowment of freedom against the Giver of it. Instead of enhancing and extending his freedom by his disobedience, however, man’s first exercise of his will apart from God brought him into bondage to a new master, sin (Ro 6:17, 18; 7:14), working through a threefold agency, the world, the flesh, and the devil (1Jn 2:16, 17; 3:8). Thus sin is not the true master of men, but a usurper, ruling with rigor, albeit the rule is disguised so that not even the wisest seems capable of recognizing it apart from the teaching of the Spirit of God."

Long my imprisoned spirit lay
Fast bound in sin and nature's night;

Thine eye diffused a quickening ray,
I woke, the dungeon flamed with light;

My chains fell off, my heart was free;

I rose, went forth, and followed Thee.

Galatians 5:13 For you were called to freedom, brethren; only do not turn your freedom into an opportunity for the flesh, but through love serve one another.

Comment: Paul says our liberty in Christ has limits imposed by our consideration of others.

James 1:25 (note) But one who looks intently at the perfect law, the law of liberty, and abides by it, not having become a forgetful hearer but an effectual doer, this man shall be blessed in what he does.

James 2:12 So speak and so act, as those who are to be judged by the law of liberty.

1 Peter 2:16 (note) Act as free men, and do not use your freedom as a covering for evil, but use it as bondslaves of God.

Comment: Real "freedom" is a marvelous paradox for it entails enslavement to God!

2 Peter 2:19 (note) promising them freedom while they themselves are slaves of corruption; for by what a man is overcome, by this he is enslaved.

Comment: Christian liberty is far removed from the fleshy license which these false teachers promise their foolish followers. John Bunyan (1628-88), author of Pilgrim's Progress, suffered in Bedford jail for his faith so was especially qualified to write on the subject of freedom

Wherefore, though the Christian, as a Christian, is the only man at liberty, as called thereunto of God; yet his liberty is limited to things that are good: he is not licensed thereby to indulge the flesh.

There is one use of eleutheria in the Septuagint...

Leviticus 19:20 'Now if a man lies carnally with a woman who is a slave acquired for another man, but who has in no way been redeemed, nor given her freedom, there shall be punishment; they shall not, however, be put to death, because she was not free.

Freedom is presented as a signal blessing of the economy of grace, and these false teachers are turning the grace of God into licentiousness, continually promising those “trying to escape” the struggles of life, the very freedom they themselves do not possess. For example they may teach false doctrines such as "Freedom in Christ means “doing your own thing” or “having it your way”, a devilish doctrine that is the very essence of sin and rebellion against the will of God and His holiness.

In stark contrast the freedom Jesus Christ offers is enjoying fulfillment IN the will of God. It is freedom and inherent Spirit given ability to live as one SHOULD, not as one PLEASES! Our victory in Christ is over death and the power of sin (1Cor 15:55, 56, 57) and frees the redeemed to achieve their greatest human potential to the glory of God.

The Quaker Rufus Jones, paraphrasing Aristotle, said,

“The true nature of a thing is the highest that it can become.”

Jesus Christ frees us to become our very best for God in this fleeting life, and then to be like Him in the next. These false teachers brought their followers into bondage by means of the LIE, whereas our Lord Jesus Christ brings men into freedom by means of the TRUTH. teaching the basic spiritual principles that "you will know the truth, and the truth will make you free."  (Jn 8:31, cp Jn 17:17) and the opposite principle that "everyone who commits (present tense = habitually, as their lifestyle) sin is the slave of sin." (Jn 8:34)

The false teachers promise freedom, but their promotion of licentiousness only brings bondage for freedom can never be found in the flesh, but only in God’s Spirit (contrast those in Jude 1:19). Unqualified freedom in any area of human life is deceptive and deadly.

As A W Tozer said...

Freedom is liberty within bounds: liberty to obey holy laws, liberty to keep the commandments of Christ, to serve mankind, to develop to the full all the latent possibilities within our redeemed natures. True Christian liberty never sets us free to indulge our lusts or to follow our fallen impulses. (God Tells the Man Who Cares. 1992, page 185)

Freedom isn’t found in what Jesus can give us, but only in Jesus Himself. Those who live by God’s truth enter into more and more freedom, but those who live by lies experience more and more bondage, until

the latter end is worse with them than the beginning (see note 2 Peter 2:20)

To reiterate, the freedom offered by these teachers is a false freedom, a freedom that tragically (ironically) only leads to bondage. It is based on false promises, empty words that sound exciting but that have no divine authority behind them. It is offered by false Christians (wolves in sheep's clothing) who were involved in a false experience. From start to finish, this brand of  freedom is clearly the work of our adversary, the devil (Jn 8:44).

The writer of Hebrews warns us to beware of the deceitfulness of sin (Heb 3:13-note).

Sin always promises freedom but in the end brings bondage. It promises life but instead brings death. Sin has a way of gradually binding a person until there is no way of escape, apart from the gracious intervention of the Lord. Even the bondage that sin creates is deceitful, for the people who are bound actually think they are free! Too late they discover that they are prisoners of their own appetites and habits.

Wuest has this note...

The liberty spoken of in Gal 5:1 is liberty from the Mosaic law, not liberty to do as one pleases. The one set at liberty from the law is under a stronger and more effective compulsion, namely, divine love as ministered to the yielded saint by the Holy Spirit (Gal 5:13). These false teachers, not being saved and therefore not knowing grace, misrepresented the latter as license to sin.

John Piper has a reasoned discussion of this section noting that

false teachers were right to promise people freedom. The call to freedom is at the heart of New Testament faith. But this was not a call to give free reign to your passions. For then you are really a slave of corruption as verse 19 says. The apostolic call to freedom recognizes 1) that Christ had died to free us from the guilt and power of sin; 2) that we are free from the law in the sense that we need no longer strive to keep it in our own strength; and 3) we are given new hearts by the Holy Spirit so that freely we delight in holiness. But everywhere this gospel of freedom was preached false teachers distorted it. And 2Pe 3:16 [note] shows that the writings of the apostle Paul were a sitting duck for this distortion. It says, "There are some things in them hard to understand, which the ignorant and unstable twist to their own destruction." The false teachers take the unstable souls (cf 2Pe 2:14-note) and teach how to use the letters of Paul to justify their view of sexual freedom. Paul already knew that his teaching about freedom was open to this abuse and he warned against it. For example, in Gal 5:13 he says: "You were called to freedom, brethren; only do not use your freedom as an opportunity for the flesh, but through love be servants of one another." But the false teachers were doing just that, using their freedom as an opportunity to indulge their love for money and their love for praise and the love for sexual pleasure. They probably quoted Gal 5:1 with great power among the new and unstable converts: "For freedom Christ has set us free; stand fast therefore and do not submit again to a yoke of slavery!" "Away with the enslaving rules that govern the life of the body! You are not under law; you are under grace!" But they probably neglected entirely those other teachings of Paul, "If you live according to the flesh you will die, but if by the Spirit you put to death the deeds of the body you will live" (Ro 8:13-note). So Peter blasts the trumpet of warning: they are twisting the Scriptures to their own destruction and their promised freedom is a bondage to corruption. (Better Never to Have Known the Way)

Torrey's Topic
Christian Liberty

Foretold -Isaiah 42:7; 61:1

CONFERRED
By God -Colossians 1:13
By Christ -Galatians 4:3-5; 5:1
By the Holy Spirit -Romans 8:15; 2Co 3:17
Through the gospel -John 8:32
Confirmed by Christ -John 8:36
Proclaimed by Christ -Isaiah 61:1; Luke 4:18
The service of Christ is -1 Corinthians 7:22

IS FREEDOM FROM
The law -Romans 7:6; 8:2
The curse of the law -Galatians 3:13
The fear of death -Hebrews 2:15
Sin -Romans 6:7,18
Corruption -Romans 8:21
Bondage of man -1 Corinthians 9:19
Jewish ordinances -Galatians 4:3; Colossians 2:20
Called the glorious liberty of the children of God -Romans 8:21
Saints are called to -Galatians 5:13

SAINTS SHOULD
Praise God for -Ps 116:16,17
Assert -1Co 10:29
Walk in -Psalms 119:45
Stand fast in -Ga 2:5; 5:1
Not abuse -Galatians 5:13; 1 Peter 2:16
Not offend others by -1Corinthians 8:9; 10:29,32

The gospel is the law of -James 1:25; 2:12

FALSE TEACHERS
Promise, to others -2 Peter 2:19
Abuse -Jude 1:4
Try to destroy -Ga 2:4

The wicked, devoid of -Jn 8:34; Ro 6:20
Typified -Lv 25:10-17; Ga 4:22, 23, 24, 25, 26,31

WHILE THEY THEMSELVES ARE SLAVES OF CORRUPTION (ruin, destruction, disintergration, rottenness): autoi douloi huparchontes (PAPMPN) tes phthoras: (Jn 8:34; Ro 6:12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22; Titus 3:3)

Literally "themselves being bondservants of the corruption."

These false teachers first come as a trusted guest, linger to become an appealing host, and remain to enslave their unwitting victims!

Since these false teachers have denied Jesus Christ Who purchased with His own blood enslaved sinners from the power of sin (2Pe 2:1), they have in effect denied the only Source of spiritual freedom (Jn 8:31, 32, 36, Ro 8:2-note, Ga 5:1). Writing to Titus Paul reiterates every man's condition who refuses God's offer of forgiveness in Christ...

For we also once were foolish ourselves, disobedient, deceived, enslaved to various lusts and pleasures, spending our life in malice and envy, hateful, hating one another. (see note Titus 3:3)

A good rule of thumb by which to judge whether a teacher is true or false is to listen to what they say about the Cross. When any teacher does not put the Cross at the center of his or her teaching, beware! Turn from that teacher. Our redemption is in the blood. Jesus bought us with His blood.

They themselves (the false teachers) are unable to deliver the freedom they promise, because they themselves are (continuously enslaved to the very corruption which their followers are also trying to escape. You cannot set someone free if you are in bondage yourself, and these false teachers were in bondage to sin. They professed to be born again but had never really been redeemed (set free) themselves as proven by their permanent condition of enslavement! A profound irony of sin is evident here: the quest for freedom from God leads only to slavery to sin and self. True freedom from sin involves joyful “slavery” to God (cf. Ro 6:18-note). The apostate ministers talk a lot about freedom, but they mean freedom from divine authority and freedom to sin. Actually, this is not liberty but the worst form of bondage. They themselves are slaves of corruption. Bound by the chains of evil lusts and habits, they are powerless to break free.

Are - Notice this verb is in the present tense which indicates their continual enslavement to sin, their master,

Slaves (1401)  (doulos from deo = to bind so doulos = one bound to another) is one who is in bondage or bound to another and thus describes the horrible state of being completely controlled by "sin".

Doulos is the most abject, servile form of slavery. The "doulos" is the possession of his master (the master in context being personified by whatever specific sin it is that conquers him) and is obligated to do "sin's" will, They should have been bond servants of Jesus Christ (1Pe 2:!6-note, etc) but instead chose to to have "corruption" as their master.

As Matthew Henry comments...

Their own lusts have gotten a complete victory over them, and they are actually in bondage to them (Ro 6:16-note), making provision for the flesh (Ro 13:!4-note) to satisfy its cravings, comply with its directions, and obey its commands. Their minds and hearts are so far corrupted and depraved that they have neither power nor will to refuse the task that is imposed on them. They are conquered and captivated by their spiritual enemies, and yield their members servants of unrighteousness (Ro 6:13-note).

Corruption (5356) (phthora from phtheiro = to destroy by means of  dissolution which in turn is brought about by internal not external decay) (3/8 NT uses in 2Peter 1:4, 2:12, 19) describes a state of ruin or destruction with the implication of disintegration, decay or rotting (like fruit or vegetables that you leave in the refrigerator crisper for months! What a picture of the hearts of these men.). In context Peter is using it to describe the  "rotting" of the morals and loss of integrity that results from a slow, inexorable internal decay or as Bishop Moule phrases it men "on the way to final ruin".  The resultant state represents a departure from the original or from what is pure or correct.

Hiebert points out that

corruption denotes not merely the decay which sin produces in this life; it also involves that spiritual corruption which leads to perdition.

In his opening comments Peter reminded the believers that...

by these (His own glory and excellence) He has granted (perfect tense = permanence of these divine gifts) to us His precious and magnificent promises, in order that by them you might become partakers of the divine nature, having escaped the corruption (phthora) that is in the world by lust. (see note 2 Peter 1:4)

As Matthew Henry so correctly said...

Grace does not run in the blood, but corruption does. A sinner begets a sinner, but a saint does not beget a saint.

FOR BY WHAT A MAN IS OVERCOME: o gar tis hettetai (3SRPI):(2Pe 2:20; Isa 28:1; Je 23:9; 2Ti 2:26)

Thomas Merton said that...

Every man becomes the image of the man he adores. He whose worship is directed to a dead thing becomes a dead thing. He who loves corruption rots. He who loves a shadow becomes, himself, a shadow.

Peter restates the same principle Paul taught in Romans --

Do you not know that when you present yourselves to someone as slaves for obedience, you are slaves of the one whom you obey, either of sin resulting in death, or of obedience resulting in righteousness? (see note Romans 6:16)

You are a slave to whatever masters you. Are you mastered by anything? by any possession? by any person? Many believe that freedom means doing anything they want. But no one is ever completely free in that sense. The freedom Christ brings is freedom from sin, not freedom to do whatever we want. Too often freedom from rules, structure, or obedience leads to an addiction or preoccupation with the new pleasures freedom offers. But these actions can quickly enslave a person. If people refuse to follow God, their only option is to follow Satan and their own sinful desires and become enslaved to what their bodies want. Only Christ promises and delivers true freedom, for only those who surrender their lives to Christ as Savior and Lord are set free from slavery to sin.  True freedom from the bondage to sin is found in our enslavement to Christ, the Lord of all.

Overcome (2274) (hettao or hettaomai or hessaomai from hetton = less, inferior) first means to be less or inferior. The idea is to be put to the worse and hence to be defeated or conquered. To succumb. To be vanquished, subdued and enslaved or overcome as in a conflict or a lawsuit. To be forced to yield. The idea is of suffering a defeat that so that what conquers now has mastery over the defeated party.

Hettao means to be vanquished as in a military battle alluding to the ancient law of war in which those who were defeated were taken captive by the conquerors and became their servants.

Hettao is used in the NT only in this verse and 2Pe 2:20 (note). in Nestle-Aland, but in KJV is also used in 2Co 12:13 where hettao means to be treated as inferior to or worse than. To be made to feel less important, be treated worse.

Hettao is used 13 times in the Septuagint (LXX) - Isa. 8:9; 13:15; 19:1; 20:5; 30:31; 31:4, 9; 33:1; 51:7; 54:17; Jer. 48:1; Da 6:5, 8.

Webster has a parallel thought stating that "overcome" means get the better of by force or strategy and implies gaining mastery over the one conquered. Now don't you have a better picture of what is going on in the hearts and lives of these false teachers? They are may look very successful but they are not to be envied because they are "defeated" men!

Hettao is in the perfect tense which signifies that they had been overcome at some point of time in the past and were still still overcome. The perfect tense speaks of the permanence of their condition..

Josephus provides us with a helpful illustration of the verb hettao describing Jacob as  being overcome by his love for Rebekah...

Jacob was quite overcome (hettao), not so much by their kindred, nor by that affection which might arise thence, as by his love to the damsel, and his surprise at her beauty, which was so flourishing, as few of the women of that age could vie with. He said then, "There is a relation between thee and me, elder than either thy or my birth, if thou be the daughter of Laban (The works of Josephus Ant I, xix 5)

Adam Clarke comments that the idea of overcome...

is an allusion to the ancient custom of selling for slaves those whom they had conquered and captivated in war. The ancient law was, that a man might either kill him whom he overcame in battle, or keep him for a slave. These were called servi, slaves, from the verb servare, to keep or preserve. And they were also called mancipia, from manu capiuntur, they are taken captive by the hand of their enemy. Thus the person who is overcome by his lusts is represented as being the slave of those lusts (see Ro 6:16-note).

William Barclay records that...

Seneca said, "To be enslaved to oneself is the heaviest of all servitudes." Persius spoke to the lustful debauchees of his day of "the masters that grow up within that sickly breast of yours." These teachers were offering liberty when they themselves were slaves, and the liberty they were offering was the liberty to become slaves of lust. (Barclay, W: The Daily Study Bible Series. The Westminster Press or Logos)

BY THIS HE IS ENSLAVED: touto dedoulotai (3SRPI):

Sin Always Enslaves

Several thousand years earlier Solomon (in context speaking of those trapped in the sin of sexual immorality) warned that sin enslaves explaining that...

His own iniquities will capture the wicked, and he will be held with the cords of his sin. (Pr 5:22-notes)

Solomon also described sinners as those who...

lie in wait for their own blood. They ambush ("booby trap" NLT) their own lives. (Pr 1:18) (Beloved, sin no matter how alluring and pleasurable is always a deadly, deceptive trap - cp Heb 3:13- note, Jas 1:15-note)

Jesus answering the Jews who had supposedly "believed" in Him (compare Jn 8:30, 31, 32 and Jn  8:40, 43, 44, 45, 46, 59 - notice His audience never changes!) ...

Truly, truly, I say to you, everyone who commits (present tense  = habitually) sin is (present tense) the slave of sin. (Jn 8:34)

Paul writing to the the saints at Rome...

Do you not know that when you present yourselves to someone as slaves for obedience, you are slaves of the one whom you obey, either of sin resulting in death, or of obedience resulting in righteousness? (Ro 6:16-note)
 

I see a different law in the members of my body, waging war against the law of my mind, and making me a prisoner of the law of sin which is in my members. (Ro 7:23-note)

Comment: The motif of bondage and freedom is central to the teaching of Paul, and it takes two forms: bondage to law and bondage to sin and death.

In Paul's last known written communication, explaining how the Lord's bondservant should conduct himself writes that he should do so...

with gentleness correcting those who are in opposition (eg, as surely the "disciples" of such false teachers would be), if perhaps God may grant them repentance leading to the knowledge of the truth, and they may come to their senses and escape from the snare of the devil (compare the snare these false teachers had laid for their foolish audience), having been held captive by him to do his will. (see notes 2Ti 2:25; 26)

So what defeats these men brings them into a permanent state of bondage as indicated by Peter's use of the perfect tense.

Enslaved (1402) (douloo - see study of doulos) means to bring someone into a state of absolute obedience and thus to bring into bondage, to enslave, to make someone a slave. The idea is to be held and controlled against one’s will. Figuratively (all NT uses except Acts 7:6) douloo means to gain control over someone. To become servant, to make someone a slave or to become a slave, to serve. The imagery derives directly from the ancient practice of enslaving an enemy defeated in battle as a prisoner! And so douloo describes not so much a relation of service as primarily one of dependence upon, or bondage to, something.

Vine writes that douloo...

signifies to fulfill the duties of a slave, for whom there was no choice either as to the kind or length of his service.

The TDNT has an interesting comment on the background of this Greek word group noting that...

Greeks have a strong sense of freedom. Personal dignity consists of freedom. There is thus a violent aversion to bondage. Service may be rendered to the state, but by free choice. Slavery is scorned and rejected. This explains the fierceness with which the Greeks fought for political independence. The only slavery Plato will allow is to the laws. The laws, however, represent the goal of humanity, so that slavery to law is in no way derogatory. Aristotle shows a similar scorn for slavery; for him slaves have no part in the state or true service to it. The Stoics have a broader view of service. Zeus himself summons us to it, so that, while free in relation to all people, we are unconditionally bound to all. Yet the Stoic would never call himself the doúlos theoú; he moves through the world as basileús and despótēs, the very opposite of the doúlos. This is the characteristic of the wise. Those who are not wise are slaves, no matter what the form of their bondage (cf. Epictetus, Plutarch, and Philo). This survey shows that the group has no religious significance for the Greeks. It acquires this as Near Eastern religions win new adherents and in so doing change the Greek view of God and our relationship to him. (Kittel, G., Friedrich, G., & Bromiley, G. W.  Theological Dictionary of the New Testament. Eerdmans)

There are 8 uses of douloo in the NT (see below) and 2 in the Septuagint (LXX) - Ge 15:13; Pr 27:8.

Genesis 15:13 And God said to Abram, "Know for certain that your descendants will be strangers in a land that is not theirs, where they will be enslaved (Hebrew = abad = to serve; Lxx = douloo) and oppressed four hundred years.
 

Acts 7:6 (quoting Ge 15:13 above) "But God spoke to this effect, that his offspring would be aliens in a foreign land, and that they would be enslaved and mistreated for four hundred years.

Romans 6:18 (note) and having been freed from sin, you became slaves (to be subdued by or subjugated to) of righteousness.

Comment: Paul calls upon his readers to be freed from the slavery of sin that they might find the glorious freedom of a higher slavery. They are to be slaves to God (verse below).

Romans 6:22 (note) But now having been freed from sin and enslaved to God, you derive your benefit, resulting in sanctification, and the outcome, eternal life.

1Corinthians 7:15 (context refers to marriage) Yet if the unbelieving one leaves, let him leave; the brother or the sister is not under bondage in such cases, but God has called us to peace.

1 Corinthians 9:19 For though I am free from all men, I have made myself a slave to all, that I might win the more.

Comment: The idea is that Paul voluntarily gave up personal rights for the sake of his work for others.

Galatians 4:3 So also we, while we were children, were held in bondage (to be dependent) under the elemental things of the world.

Titus 2:3 (note) Older women likewise are to be reverent in their behavior, not malicious gossips, nor enslaved to much wine, teaching what is good,

Comment: Expositor's Greek Testament has a pithy comment writing that "It is proved by experience that the reclamation of a woman drunkard is almost impossible."

2 Peter 2:19 (note) promising them freedom while they themselves are slaves of corruption; for by what a man is overcome, by this he is enslaved.

Wiersbe rightly warns us that...

The cords of sin get stronger the more we sin, yet sin deceives (Heb 3:13- note) us into thinking we're free and can quit sinning whenever we please. As the invisible chains of habit are forged, we discover to our horror that we don't have the strength to break them. Millions of people in our world today are in one kind of bondage or another and are seeking for deliverance, but the only One who can set them free is Jesus Christ. "Therefore if the Son makes you free, you shall be free indeed" (John 8:36, NKJV).

These deceived lying false teachers promise freedom, perhaps freedom from laws or other restraints (even conscience) of the sinful tendencies found in our flesh nature inherited from Adam. For example there is a teaching making the rounds in evangelical circles that if we are once saved we are always saved (this part of the teaching is sound) and now that we are under grace and saved forever, we can continue sinning habitually.

John would counter this "soft gospel" (really a "no gospel") warning us that

Everyone who practices (present tense = habitually, as a lifestyle) sin also practices (present tense = habitually, as a lifestyle)  lawlessness; and sin is lawlessness...8 the one who practices (present tense = habitually, as a lifestyle)  sin is of the devil; for the devil has sinned from the beginning. The Son of God appeared for this purpose, to destroy the works of the devil. 9 No one who is born of God practices (present tense = habitually, as a lifestyle)  sin, because His seed abides in him; and he cannot sin (present tense = habitually, as a lifestyle), because he is born of God. 10 By this the children of God and the children of the devil are obvious: anyone who does not practice (present tense = habitually, as a lifestyle)  righteousness is not of God, nor the one who does not love his brother." (read the entire chapter 1John 3)

Paul implies that he encountered a similar error in Corinth (read 1Cor 6:12ff).

Jesus warned that

Not everyone who says to Me, 'Lord, Lord,' will enter the kingdom of heaven, but he who does the will of My Father who is in heaven will enter. Many will say to Me on that day, 'Lord, Lord, did we not prophesy in Your name, and in Your name cast out demons, and in Your name perform many miracles?' And then I will declare to them, 'I never knew you; DEPART FROM ME, YOU WHO PRACTICE (present tense) LAWLESSNESS  (see note Matthew 7:21, See also Torrey's interesting topical listing of Scriptures on "Self Delusion")

Peter says the very ones who speak of freedom are slaves. These false teachers talk of religion and freedom but they do not truly know the Son of God and are not known by Him (as the passage in Matthew 7 teaches). Jesus taught that

If you continue in My word, then you are truly disciples of Mine; 32 and you will know the truth, and the truth will make you free. (eleutheroo = verb form of word Peter used for the "freedom" the false teachers promised)" ...34..."Truly, truly, I say to you, everyone who commits (present tense = habitually, as their lifestyle) sin is the slave (doulos) of sin. (Jn 8:31-37)

Wuest writes...

Strachan, commenting on the words, "while they promise them liberty," says: "Doubtless that Antinomianism (against law, thus lawlessness, not responsible to law) is indicated to which the doctrine of grace has ever been open. Compare Galatians 5:13. It arises from the ever-recurring confusion of liberty and license. The training of conscience is contemporaneous with the growth of Christian character. The Pauline teaching, which abrogated external legality, was open to abuse, and might easily be dangerous to recent converts from heathenism." The liberty spoken of in Galatians 5:1 is liberty from the Mosaic law, not liberty to do as one pleases. The one set at liberty from the law is under a stronger and more effective compulsion, namely, divine love as ministered to the yielded saint by the Holy Spirit (Gal. 5:13). These false teachers, not being saved and therefore not knowing grace, misrepresented the latter as license to sin. "Servants" is Doulos, "slaves." The word is a designation of the most abject, servile form of slavery. (Wuest, K. S. Wuest's Word Studies from the Greek New Testament: Eerdmans or Logos)

Bible Knowledge Commentary adds that

The techniques of false teachers are only workable with the naive, for the heretics are like a 300-pound man selling diet books— they promise . . . freedom but are themselves hopelessly enslaved by depravity (Jn 8:34, 35, 36). Their empty and boastful promises of liberty are reminiscent of Satan’s words to Eve (Ge 3:5). Slavery is not merely chattel ownership but is the mastery of one’s will by any person, idea, or substance (Ro 6:16-note; 1Cor 6:12b). (bolding & colors added)

Torrey's Topic
Self Delusion

A characteristic of the wicked -Psalms 49:18

Prosperity frequently leads to -Psalms 30:6; Hosea 12:8; Luke 12:17-19

Obstinate sinners often given up to -Psalms 81:11,12; Hosea 4:17; 2 Thessalonians 2:10,11

EXHIBITED IN THINKING THAT
Our own ways are right -Proverbs 14:12
We should adhere to established wicked practices -Jeremiah 44:17
We are pure -Proverbs 30:12
We are better than others -Luke 18:11
We are rich in spiritual things -Revelation 3:17
We may have peace while in sin -Deuteronomy 29:19
We are above adversity -Psalms 10:6
Gifts entitle us to heaven -Matthew 7:21,22
Privileges entitle us to heaven -Matthew 3:9; Luke 13:25,26
God will not punish our sins
Psalms 10:11; Jeremiah 5:12
Christ shall not come to judge
2 Peter 3:4
Our lives shall be prolonged
Isaiah 56:12; Luke 12:19; James 4:13

Frequently preserved in, to the last
Matthew 7:22; 25:11,12; Luke 13:24,25

Fatal consequences of
Matthew 7:23; 24:48-51; Luke 12:20; 1 Thessalonians 5:3

Exemplified
Ahab
1 Kings 20:27,34
Israelites
Hosea 12:8
Jews
John 8:33,41
Church of Laodicea
Revelation 3:17
Babylon
Isaiah 47:7-11

Torrey's Topic
Spiritual Bondage