Contradiction with Exodus 20:13
"Thou shalt not kill." contradicts the context of warfare and taking lives that surrounds Numbers 31:51.
Exodus 20:13: Thou shalt not kill.
Contradiction with Matthew 5:44
"But I say unto you, Love your enemies, bless them that curse you..." contrasts with the notion of conflict present in Numbers 31:51.
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 Isaiah 2:4
"And they shall beat their swords into plowshares, and their spears into pruninghooks..." contrasts with the notion of warfare found in Numbers 31:51.
Isaiah 2:4: And he shall judge among the nations, and shall rebuke many people: and they shall beat their swords into plowshares, and their spears into pruninghooks: nation shall not lift up sword against nation, neither shall they learn war any more. [pruninghooks: or, scythes]
Contradiction with Romans 12:17
"Recompense to no man evil for evil..." contradicts the approval of taking war spoils as implied in Numbers 31:51.
Romans 12:17: Recompense to no man evil for evil. Provide things honest in the sight of all men.
Contradiction with James 1:20
"For the wrath of man worketh not the righteousness of God." challenges the idea of righteous judgment or conflict evident in Numbers 31:51.
James 1:20: For the wrath of man worketh not the righteousness of God.