1-john 5:17

All unrighteousness is sin - Πασα αδικια, Every act contrary to justice is sin - is a transgression of the law which condemns all injustice.

All unrighteousness is sin ... - This seems to be thrown in to guard what he had just said, and there is "one" great and enormous sin, a sin which could not be forgiven. But he says also that there are many other forms and degrees of sin, sin for which prayer may be made. Everything, he says, which is unrighteous - ἀδικία adikia - everything which does not conform to the holy law of God, and which is not right in the view of that law, is to be regarded as sin; but we are not to suppose that all sin of that kind is of such a character that it cannot possibly be forgiven. There are many who commit sin who we may hope will be recovered, and for them it is proper to pray. Deeply affected as we may be in view of the fact that there is a sin which can never be pardoned, and much as we may pity one who has been guilty of such a sin, yet we should not hastily conclude in any case that it has been committed, and should bear constantly in mind that while there is one such sin, there are multitudes that may be pardoned, and that for them it is our duty unceasingly to pray.

5:17 All deviation from perfect holiness is sin; but all sin is not unpardonable.