For that which I am doing, I do not understand; for I am not practicing what I would like to do, but I am doing the very thing I hate. (Romans 7:15)
Paul's proof that sin still indwelt him was in the reality that that which I am doing, I do not understand; for I am not practicing what I would like to do.
Ginõskõ (understand) has the basic meaning of taking in knowledge in regard to something or someone, knowledge that goes beyond the merely factual. By extension, the term frequently was used of a special relationship between the person who knows and the object of the knowledge. It was often used of the intimate relationship between husband and wife and between God and His people. Paul uses the term in that way to represent the relationship between the saved and the Savior: "Now that you have come to know God, or rather to be known by God, how is it that you turn back again to the weak and worthless elemental things, to which you desire to be enslaved all over again?" (Gal. 4:9). By further extension, the word was used in the sense of approving or accepting something or someone. "If anyone loves God," Paul says, "he is known [accepted] by Him" (1 Cor. 8:3).
That seems to be the meaning here and is consistent with the last half of the sentence. Paul found himself doing things he did not approve of. It was not that he was unable to do a particular good thing but that when he saw the fullness and grandeur of God's law, he was not able to measure up completely. It was not that he could never accomplish any good at all, nor that he could never faithfully obey God. The apostle was rather expressing an inner turmoil of the most profound kind, of sincerely desiring in his heart to fulfill the spirit as well as the letter of the law (see 7:6) but realizing that he was unable to live up to the Lord's perfect standards and his own heart's desire.
It was not Paul's conscience that was bothering him because of some unforgiven sin or selfish reluctance to follow the Lord. It was his inner man, recreated in the likeness of Christ and indwelt by His Spirit, that now could see something of the true holiness, goodness, and glory of God's law and was grieved at his least infraction or falling short of it. In glaring contrast to his preconversion self-satisfaction in thinking himself blameless before God's law (Phil. 3:6), Paul now realized how wretchedly short of God's perfect law he lived, even as a Spirit-indwelt believer and an apostle of Jesus Christ.
That spirit of humble contrition is a mark of every spiritual disciple of Christ, who cries out, "Lord, I can't be all you want me to be, I am unable to fulfill your perfect, holy, and glorious law." In great frustration and sorrow he painfully confesses with Paul, I am not practicing what I would like to do...