FOR THIS REASON GOD GAVE THEM OVER TO DEGRADING PASSIONS: Dia touto paredoken (3SAAI) autous o theos eis pathe atimias:

"For this reason" is a Greek phrase composed of two words (dia touto) variously translated in the NAS as "for this cause", "for this purpose", "for because of this", "therefore" and functions as a term of conclusion.  As you become more familiar with inductive Bible study you will develop the habit of pausing and asking "for what reason?". In the present case the answer is straightforward - they made a bad choice to exchange the truth of God for a lie which progressed to idol worship. In the previous verses Paul had stated their speculative belief and he now proceeds to show the practical outworking of their belief in their conduct in some of the most sobering and fearful passages in all of Scripture.

Moule introduces up this section writing that God...

As if animated by the word of benediction, he returns to denounce “the abominable thing which God hateth” with still more terrible explicitness. For this reason, because of their preference of the worse to the infinite Good, God gave them up to passions of degradation; He handed them over, self-bound, to the helpless slavery of lust; to “passions,” an eloquent word which indicates how the man who will have his own way is all the while a “sufferer,” though by his own fault: the victim of a mastery which he has conjured from the deep of sin. (Moule, C. G. Handley: The Epistle of St Paul to the Romans)

"Gave...over" (3860) (paradidomi from para = beside + didomi = to give so literally to give beside) is a very strong Greek verb meaning to hand someone over to the power and authority of another. It is that act of God whereby He hands over the entire human race for judgment because of their sins.

"God gave them over" is the second of three occurrences of paradidomi in Romans 1. The restraint of God that might have kept people living in pure relationships with each other was removed. This phrase "God gave them over" should put the fear of the Lord into the heart and mind of every thinking person. We may even be so deceived that we think we are in control but sin deceives and when we think we are not in the grips or power of sin we are completely deceived.

John MacArthur explains God's giving...over writing that...

God’s giving over sinful mankind has a dual sense. First, in an indirect sense God gave them over simply by withdrawing His restraining and protective hand, allowing the consequences of sin to take their inevitable, destructive course. Sin degrades man, debases the image of God in which he is made, and strips him of dignity, peace of mind, and a clear conscience. Sin destroys personal relationships, marriages, families, cities, and nations It also destroys churches... Fallen men are not concerned about their sin but only about the pain from the unpleasant consequences sin brings Someone has well said that sin would have fewer takers if the consequences were immediate....

In a second, direct sense God gave…over rebellious mankind by specific acts of judgment. The Bible is replete with accounts of divine wrath being directly and supernaturally poured out on sinful men. The flood of Noah’s day and the destruction of Sodom and Gomorrah, for example, were not indirect natural consequences of sin but were overt supernatural expressions of God’s judgment on gross and unrepented sin. God often allows men to go deeper and deeper into sin in order to drive them to despair and to show them their need of Him. (MacArthur, J. Romans. Chicago: Moody Press)

"Degrading" (819) (atimia from átimos = without honor) means worthy of dishonor (condition of suffering loss of esteem and of enduring reproach = emphasizes the loss of honor that one once enjoyed = cf man originally created in God's image), disgrace (to be a source of shame to & often implies humiliation and sometimes ostracism), ignominy (deep personal humiliation and disgrace, disgraceful or dishonorable conduct, quality, or action. This noun stresses humiliation). KJV translates "atimia" as "vile" which Webster defines as morally despicable or abhorrent, physically repulsive, disgustingly or utterly bad. Compared to "base" or "low" (morally speaking) "vile" is the strongest of these words and tends to suggest disgusting depravity or filth. What a nasty word! And God gave men and women over to this quality of passions!

Barnes comments that...

The great object of the apostle here, it will be remembered, is to shew the state of the pagan world, and to prove that they had need of some other way of justification than the law of nature. For this purpose, it was necessary for him to enter into a detail of their sins. The sins which he proceeds to specify are the most indelicate, vile, and degrading which can be charged on man. But this is not the fault of the apostle. If they existed, it was necessary for him to charge them on the pagan world. His argument would not be complete without it. The shame is not in specifying them, but in their existence; not in the apostle, but in those who practiced them, and imposed on him the necessity of accusing them of these enormous offences. It may be further remarked, that the mere fact of his charging them with these sins is strong presumptive proof of their being practiced. If they did not exist, it would be easy for them to deny it, and put him to the proof of it. No man would venture charges like these without evidence; and the presumption is, that these things were known and practiced without shame. But this is not all. There is still abundant proof on record in the writings of the pagan themselves, that these crimes were known and extensively practiced.

Passions (3806) (pathos from páscho = suffer) (3 uses: Romans; Colossians; 1 Thessalonians) primarily denotes whatever one suffers or experiences in any way; hence, an affection of the mind, a passionate desire. Pathos was used by the Greeks to describe either good or bad desires but in the NT pathos always refers to bad desires, especially of a sexual nature.  Pathos means excited emotion, uncontrollable desire, compelling feelings, overpowering urges.

Pathos denotes not so much the violence of the feeling as its ungovernable nature. Note the derivation from the verb pascho to suffer which expresses the lustful feeling the individual suffers.

A passion is a drive or force that does not rest until satisfied. These are internal desires (emanating from our fallen sin nature) cause the victim to suffer and that have to be satisfied or they drive you crazy. A passion describes intense emotion compelling action; intense, driving, or overmastering feeling or conviction; ardent affection; sexual desire or an emotion that is deeply stirring or ungovernable. The word "desires" (when used as noun as in the present context) means to have a longing for and stresses the strength of feeling and often implies strong intention or aim; conscious impulse toward something that promises enjoyment or satisfaction in its attainment.

These degrading passions are Identified in these two verses as homosexuality, a sin indubitably condemned in Scripture (Ge 19:5; Lv 18:22-28; Dt 23:17,18; Jdg 19:22; 1Cor 6:9; Eph 4:19; 5:12; 1Ti 1:10; Jude 1:7,10). Self-will brings its own suffering. Natural laws have a self-executing power in a corresponding requital.

Pastor Ray Pritchard has an interesting comment

"Why is illicit sex singled out as the first major step away from God? The answer is not hard to find. Sex is closely related to the human spirit. The way you conduct yourself sexually is a good barometer of what's going on in your heart. After all, what is sex but the desire to be worshiped by another person? Sound strange? It shouldn't. When two people come together, they are seeking much more than physical release. At a very deep level, they are looking for love, acceptance, fulfillment, freedom and meaning in life. By giving themselves to someone else, they hope (and secretly pray) that through this self-giving, they will discover a way to fill the void within. They "worship" through sex hoping someone will "worship" them back. Sex and worship are thus closely related in their ultimate purpose. It is as if God is pulling back the covers in order to show us how empty our hearts are without him. By turning to illicit sex, instead of fulfilling our dreams we only expose the emptiness within. It never works out like we hope it will. Immorality never satisfies because it always involves deception. We lie to each other, we lie to ourselves, and ultimately we lie to God."

The descent into paganism with its focus on idolatry is always soon followed by gross immorality, especially sexual perversion. Ancient Sodom was so notorious for homosexuality that its practice has long been known as sodomy, Moses recording that...

"Now the men of Sodom were wicked exceedingly and sinners against the LORD." (Genesis 13:13)

How exceedingly wicked were the men of Sodom? Moses later records the visit of two angels to escort Lot and family out of Sodom writing that...

Before they lay down (in Lot's house), the men of the city, the men of Sodom, surrounded the house, both young and old, all the people from every quarter and they called to Lot and said to him, "Where are the men who came to you tonight? Bring them out to us that we may have relations with them." (homosexuality) But Lot went out to them at the doorway, and shut the door behind him, and said, "Please, my brothers, do not act wickedly. Now behold, I have two daughters who have not had relations with man; please let me bring them out to you, and do to them whatever you like; only do nothing to these men, inasmuch as they have come under the shelter of my roof.  But they said, "Stand aside." Furthermore, they said, "This one came in as an alien, and already he is acting like a judge; now we will treat you worse than them." So they pressed hard against Lot and came near to break the door."  (Genesis 19:4-9).

And of course we know how the "wrath of God" was revealed against the ungodliness of Sodom!

The practice of homosexuality became so widespread in ancient Greece that it was considered normal and even desirable!

As dark and depressing as this section of Romans is, the truth in these verses can bring grace to those without Christ and set captives free, just as it did to a brilliant physician in one of Richard Halverson’s Bible studies on Romans who said,

“I don’t ever remember reading the Bible, but tonight I have seen myself in Romans 1; now what do I do about it?”

As mentioned earlier, the Scripture frequently links idolatry as leading to immorality. Idolatrous worship of Baal in the OT was inevitably accompanied by immorality including the abomination of temple prostitution, involving not just females but also male cult prostitutes! When man invents a god or gods (usually plural) of his own making, he is then free to "rewrite" the rules of human conduct or at least he is deceived into thinking he can do so and that there will be no consequences (The fate of Sodom stands as a powerful testimony that God will judge sin!). Then ungodly men and women begin to pontificate the dogma on the airways and the written media that you can live anyway you want to live and that no authority, God or otherwise, has the right to place their moral constructs on you. The Ten Commandments no longer apply and are treated blithely as "10 suggestions". Want to sleep around or live together outside of marriage? Go ahead. Want to have an orgy? Go ahead. Want to legalize abortion, prostitution or gambling? Go ahead. You can indulge your wildest fantasies once you begin making the rules. That's the tragic picture of Romans 1:18-32. God gave them over to what they wanted. They made the choice to turn from God but unfortunately cannot chose to skirt God's judgment. He will repay justly.

FOR THEIR WOMEN (literally "females") EXCHANGED THE NATURAL (physical) FUNCTION FOR THAT WHICH IS UNNATURAL: ai te gar theleiai auton metellaxan (3PAAI) ten phusiken chresin eis ten para phusin:

"Women" (819 women exchanged natural function unnatural) is the Greek word thelus but is not the noble one which usually is used for "women"; but aptly denotes sex only, as in the lower creatures.

Barnes notes that...

Evidence of the shameful and disgraceful fact here charged on the women is abundant in the Greek and Roman writers.

Exchanged (3337) (metallasso from metá = change of place or condition + allásso = change) is used only in this verse and the preceding in the NT and means to cease one activity and to start something else in exchange. It denotes the giving up of one thing (the natural function of the woman, heterosexuality and child bearing) in order to receive another (the lie of lesbianism). Women became lesbians, practicing unnatural sex and knowing no shame.

The verb exchanged is aorist tense (action at a moment in time) and active voice (subject makes a choice of their will to carry out this action) indicating that these women made a deliberate choice to exchange the natural for the unnatural, which was a reflection of the influence of the degrading passions God had given them into the power of.

Expositor's Bible Commentary observes that...

Paul's use of "exchanged" is suggestive. The first exchange, that of the truth for the lie, is followed by another--the upsetting of the normal course of nature in sexual relations. Instead of using the ordinary terms for men and women, Paul substitutes "males" and "females." The irony is that this sort of bestiality finds no counterpart in the animal kingdom. Perversion is the unique contrivance of the human species.  (Gaebelein, F, et al: Expositor's Bible Commentary: Old and New Testament 12 Volumes)

"Natural" (natural) (phusikos from phúsis = nature) means pertaining to things in accordance with nature or belonging to the naturally regulated order of things. Phusikos refers to those things which one does out of instinct. The idea is that something pertains to that which is in accordance with the nature or character of that thing. Thus it is natural for both men and woman to desire heterosexual relationships.

Peter uses phusikos to describe false teachers as likened to animals whose natural destiny is to be victims of predators. (see exposition of 2 Peter 2:12-13)

"Function" (function) (chresis from chráomai = to use) describes use or the act (usage) or manner (use) of using. It can refer to the habitual or customary usage of something. Chresis was commonly used of sexual intercourse, and in this context the term could refer to nothing other than intimate sexual relations and more specifically the perverted use of one's body and not the use specified in God's plan and order for men and women who were created in His image.

"Unnatural" is the same word for "natural" (phusikos) preceded by the preposition para (3844) which means alongside, beside or contrary. Thus their acts are "contrary to natural acts". Even most pagan societies have recognized the clearly obvious fact that homosexuality is abnormal and unnatural. It is also an abnormality that is unique to man.

William Newell (in the 1920's) comments:

This passage has deep significance in this day of the "sex-craze": when, as some one says, "Human beings seem to be just beginning to realize that they are male and female." The first of Romans warns of what such a craze will end in! (Ed note: And he did not live to see the AIDS epidemic).

Paul mentions women first probably to emphasize the extent of debauchery under the wrath of abandonment, because in most cultures women are the last to fall into homosexuality and other moral aberrations!

J Vernon McGee notes that...

These are passions of dishonor and disgrace and depravity—regardless of what public opinion is today. Perversion entered into Greek life, and it brought Greece down to the dust. Go over there and look at Greece today. The glory has passed away. Why? These were their sins." (McGee, J. V. Thru the Bible commentary. Nashville: Thomas Nelson)

God abandoned them not only to idolatry, the ultimate expression of man’s spiritual degeneracy, but also to degrading passions, which he identifies in these two verses as homosexuality, the ultimate expression of man’s moral degeneracy.

When man forsakes the AUTHOR of nature,
he inevitably forsakes the ORDER of nature.

Charles Hodge wrote,

“Paul first refers to the degradation of females among the heathen, because they are always the last to be affected in the decay of morals, and their corruption is therefore proof that all virtue is lost” 

Even most pagan societies have recognized the clearly obvious fact that homosexuality is abnormal and unnatural. It is also an abnormality that is unique to man.

Hughes writes: