if I repaid with evil the one who lived in peace with me, or without cause robbed the one who opposed me,
David distinguishes two possible sins: repaying a friend with evil, and acting unjustly toward an adversary. The first is ingratitude; the second is vengeance or exploitation. He declares that he does not want to justify himself merely because the other person is an adversary. Even toward an enemy, a person has no right to commit injustice. This is a broadly applicable principle for the Christian life. The harm done to us does not sanctify our sinful response. The believer is called not to repay evil with evil and, as far as possible, to keep peace (Romans 12:17–18). David presents his conduct to God’s examination, showing that the demand for righteousness must begin with one’s own heart. We cannot pray convincingly for the stopping of evil if we ourselves knowingly practice the same evil. This verse teaches that even toward an enemy one must remain righteous and not allow the evil he has done to drive us also into wrongdoing.