Contradiction with Matthew 5:44
Contradicts by promoting love and prayer for enemies, while 2 Samuel 22:51 praises God for deliverance and conquest over enemies.
Matthew 5:44: But I say unto you, Love your enemies, bless them that curse you, do good to them that hate you, and pray for them which despitefully use you, and persecute you;
Contradiction with Romans 12:19
Contradicts by advising against seeking vengeance, leaving it to God, whereas 2 Samuel 22:51 celebrates divine vengeance granted to David.
Romans 12:19: Dearly beloved, avenge not yourselves, but [rather] give place unto wrath: for it is written, Vengeance [is] mine; I will repay, saith the Lord.
Contradiction with Proverbs 24:17
Contradicts by advising to not rejoice when enemies fall, while 2 Samuel 22:51 rejoices in overcoming adversaries.
Proverbs 24:17: Rejoice not when thine enemy falleth, and let not thine heart be glad when he stumbleth:
Contradiction with Luke 6:35
Contradicts by encouraging love for enemies without expectation of reward, contrasting the victory and mercy given to David and his descendants in 2 Samuel 22:51.
Luke 6:35: But love ye your enemies, and do good, and lend, hoping for nothing again; and your reward shall be great, and ye shall be the children of the Highest: for he is kind unto the unthankful and [to] the evil.