As a rule in the New Testament epistles, “sins” (plural) refer to the evil deeds that men do, and “sin” (singular) is the fallen nature in men (the flesh). Hence, “sins” are evil actions, whereas “sin” is the evil nature. The first is what we have done, and the second is what we are. Thus, “sins” are manifestations of “sin;” or “sins” are the product of “sin;” or “sins” are the fruit of a bad tree and “sin” is the root of that bad tree. “Sin” is more than just the old sin-nature; it is that evil nature with a will in it that is determined to gratify its lusts.
Another difference between these two things is that “sins” can be “forgiven” by the grace of God (Rom. 4:77Saying, Blessed are they whose iniquities are forgiven, and whose sins are covered. (Romans 4:7)), but “sin” is not forgiven, but rather, it is “condemned” under the righteous judgment of God (Rom. 8:33For what the law could not do, in that it was weak through the flesh, God sending his own Son in the likeness of sinful flesh, and for sin, condemned sin in the flesh: (Romans 8:3)). It is important to pay attention to this distinction when reading the epistles; if we don’t, we will come away with some mistaken ideas.