Contradiction with Romans 12:19
This verse advises not to take revenge and to leave vengeance to God, contradicting Joab's action in 2 Samuel 18:16, where he orders the pursuit of Absalom's forces to stop after Absalom's death.
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 Matthew 5:44
Jesus instructs to love enemies and pray for them, which contradicts Joab's military actions even after Absalom’s defeat.
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 Proverbs 24:17
Advises against rejoicing when an enemy falls, which contrasts with the pursuit and defeat in 2 Samuel 18:16.
Proverbs 24:17: Rejoice not when thine enemy falleth, and let not thine heart be glad when he stumbleth:
Contradiction with Ezekiel 18:23
God questions the delight in the death of the wicked, which contrasts with Joab’s end to the pursuit without concern for the lives lost.
Ezekiel 18:23: Have I any pleasure at all that the wicked should die? saith the Lord GOD: [and] not that he should return from his ways, and live?