Contradiction with Exodus 20:13
Contradicts by stating "Thou shalt not kill," whereas 1 Samuel 22:21 relates to the death of priests.
Exodus 20:13: Thou shalt not kill.
Contradiction with Matthew 5:44
Advises to "love your enemies," contradicting the act of violence in 1 Samuel 22:21.
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 6:16-17
States God hates "hands that shed innocent blood," opposing the killing described in 1 Samuel 22:21.
Proverbs 6:16-17: These six [things] doth the LORD hate: yea, seven [are] an abomination unto him: [unto...: Heb. of his soul]
Contradiction with Romans 12:17-19
Encourages not to repay evil for evil and to let God avenge, contrasting the retributive action in 1 Samuel 22:21.
Romans 12:17-19: Recompense to no man evil for evil. Provide things honest in the sight of all men.
Contradiction with James 2:13
Emphasizes mercy triumphing over judgment, conflicting with the lack of mercy in the events of 1 Samuel 22:21.
James 2:13: For he shall have judgment without mercy, that hath shewed no mercy; and mercy rejoiceth against judgment. [rejoiceth: or, glorieth]