1 John 5:17 All unrighteousness is sin, and there is a sin not leading to death: pasa adikia hamartia estin (3SPAI) kai estin (3SPAI) hamartia ou pros thanaton: (all: 1Jn 3:4 De 5:32 12:32)(and: 1Jn 5:16 Isa 1:18 Eze 18:26-32 Ro 5:20,21 Jas 1:15 4:7-10)
Amplified - All wrongdoing is sin, and there is sin which does not [involve] death [that may be repented of and forgiven].
A DESCRIPTION OF SIN
David Smith says John is giving "A gentle warning. “Principiis obsta.” Also a reassurance. “You have sinned, but not necessarily ‘unto death’.”
NET Note - Here, having implied that sins committed by believers (sins “not to death”) may be prayed for and forgiven, the author does not want to leave the impression that such sin is insignificant, because this could be viewed as a concession to the views of the opponents (who as moral indifferentists have downplayed the significance of sin in the Christian’s life). (NET Note)
Vincent on all unrighteousness - This is the character of every offence against that which is right. Every breach of duty is a manifestation of sin. Compare 1Jn 3:4, where sin is defined as ἀνομία lawlessness, and lawlessness as sin. See Rom. 6:13.
Unrighteousness (93)(adikia from a = not + dikê = right) is a condition of not being right, whether with God, according to the standard of His holiness and righteousness or with man, according to the standard of what man knows to be right by his conscience.
Barclay writes that "Adikia is the precise opposite of dikaiosune (righteousness), which means justice; and the Greeks defined justice as giving to God and to men their due. The evil man is the man who robs both man and God of their rights. He has so erected an altar to himself in the centre of things that he worships himself to the exclusion of God and man." (Daily Study Bible Online)
Sin (266)(hamartia) literally conveys the idea of missing the mark as when hunting with a bow and arrow (in Homer some hundred times of a warrior hurling his spear but missing his foe). Later hamartia came to mean missing or falling short of any goal, standard, or purpose. Hamartia in the Bible signifies a departure from God's holy, perfect standard of what is right in word or deed (righteous). It pictures the idea of missing His appointed goal (His will) which results in a deviation from what is pleasing to Him. In short, sin is conceived as a missing the true end and scope of our lives, which is the Triune God Himself. As Martin Luther put it "Sin is essentially a departure from God."
Death (2288)(thanatos) is a permanent cessation of all vital functions and thus is the end of life on earth (as we know it). The separation of the soul from the body and the end of earthly life. Spiritual death is separation from the life of God forever by dying without being born again. The first use in the Septuagint is in a well known promise from God "you shall surely die (Lxx = thanatos apothnesko).” (Ge 2:17) followed by the second use in the deceptive lie by Satan “You surely shall not die (thanatos apothnesko)!" (Ge 3:4) Death is natural to humanity as part of the created world. Death is a result of Adam’s sin (Ro 5:12). Death is universal - no one can escape it.