Contradiction with Matthew 5:44
1 Samuel 28:1 describes preparations for battle, while Matthew 5:44 teaches to love enemies and do good to those who hate you.
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
1 Samuel 28:1 involves a plan for revenge in battle, whereas Romans 12:19 instructs to leave vengeance to God.
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 Exodus 20:13
1 Samuel 28:1 involves war and potential killing, contradicting the commandment in Exodus 20:13, which says "Thou shalt not kill."
Exodus 20:13: Thou shalt not kill.
Contradiction with Isaiah 2:4
1 Samuel 28:1 speaks of impending war, whereas Isaiah 2:4 envisions a future where nations do not learn war anymore.
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 Matthew 26:52
1 Samuel 28:1 discusses preparing for battle; in contrast, Matthew 26:52 advises that those who take the sword will perish by the sword.
Matthew 26:52: Thinkest thou that I cannot now pray to my Father, and he shall presently give me more than twelve legions of angels?