Martin Luther on John 16:9, speaking of the Holy Spirit convicting the world “of sin, because they believe not on me.”
Thus both salvation and damnation hinge entirely on whether we believe or do not believe. The sentence that closes and denies heaven to all who have refused to accept this faith in Christ has already been pronounced with finality. For this unbelief retains all sin and cannot obtain forgiveness, just as faith delivers from all sin. Hence without this faith everything, including even the best works and life of which man is capable, is and remains sinful and damnable. Good works may be praiseworthy in themselves and commanded by God; but they are vitiated by unbelief and for this reason cannot please God just as all the works and life which spring from the faith of a Christian are pleasing to God. In brief, without Christ all is damned and lost; in Christ all is good and blessed. Therefore even the sin inherited from Adam and still dwelling in flesh and blood does not have to harm or damn us.
But one should not understand this to mean that sin is permitted, that one may sin and do evil without restraint. For since faith brings forgiveness of sin, and since Christ came to remove and destroy sin, it is impossible for anyone who lives openly, impenitently, and smugly in sin and according to his lusts to be a believing Christian. For where there is such a sinful life, there can be no penitence; but where there is no penitence, there can be no forgiveness of sin either, and consequently no faith, which received the forgiveness of sin. On the other hand, he who has faith in such forgiveness resists sin and does not give way to its lusts but contends against it until he is rid of it. And although we cannot be completely rid of sin in this life, although it still remains even in the saintliest people, yet believers have the comfort that this is covered by Christ’s forgiveness and is not reckoned for their damnation if they continue to believe in Christ. Here the words of St. Paul in Rom. 8:1,4 apply: “There is therefore now no condemnation for those who are in Christ Jesus, who walk not according to the flesh.” Also the words found in Gal. 5:24: “And those who belong to Christ Jesus have crucified the flesh with its passions and desires.” Behold, these are the people who are told that sin will not harm or condemn them. To the others, the unbelievers and reprobates, no message is given here.