The source of sin can be mental or physical. With the first it can be from being "alienated and hostile in mind, engaged in evil deeds" (Col 1:21). It can be "iniquity . . . and wickedness" (Eze 18:20), "unrighteousness" (Ro 6:13), or "transgression and disobedience" (Heb 2:2). In the second case it can be due to the "sinful flesh" (Ro 8:3) with "its passions and desires" (Gal 5:24). It is in our "mortal body" (Ro 6:12) in "our body of sin" (:6) so that we "obey its lusts" (:12) and are "slaves to sin" (:6). Then the Law was given and "through the Law comes the knowledge of sin" (3:20). Paul said that "the Law is spiritual, but I am of flesh, sold into bondage of sin" (7:14). But "by the works of the Law no flesh will be justified in His sight" (3:20). However, "the Law came in so that the transgression would increase; but where sin increased, grace abounded all the more" (5:20). "What the Law could not do, weak as it was through the flesh, God did: sending His own Son in the likeness of sinful flesh and as an offering for sin, He condemned sin in the flesh" (8:3). Therefore "do not let sin reign in your mortal body . . . [or] go on presenting the members of your body to sin" (6:12-13). "Sin shall not be master over you, for you are not under law but under grace" (:14).
"But God demonstrates His own love toward us, in that while we were yet sinners, Christ died for us" (Ro 5:8). "He made Him who knew no sin to be sin on our behalf, so that we might become the righteousness of God in Him" (2Co 5:21). He "gave Himself for us to redeem us from every lawless deed" (Titus 2:14) and was "offered once to bear the sins of many" (Heb 9:28). He was "delivered over because of our transgressions, and was raised because of our justification" (Ro 4:25). "If Christ is in you, though the body is dead because of sin, yet the spirit is alive because of righteousness" (8:10). "He Himself bore our sins in His body on the cross, so that we might die to sin and live to righteousness; for by His wounds you were healed" (1Pe 2:24). "Our old self was crucified with Him, in order that our body of sin might be done away with, so that we would no longer be slaves to sin" (Ro 6:6). "He Himself is the propitiation for our sins; and not for ours only but also for those of the whole world" (1Jn 2:2). Jesus said, "'This is the blood of the covenant, which is poured out for many for forgiveness of sins'" (Mt 26:28).