Contradiction with Exodus 20:13
1 Samuel 19:15 involves a plot to kill David, which contradicts the commandment "Thou shalt not kill".
Exodus 20:13: Thou shalt not kill.
Contradiction with Matthew 5:44
1 Samuel 19:15 involves seeking harm to David, contrary to the teaching of loving your 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
1 Samuel 19:15 shows an attempt at vengeance, while this verse 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 Proverbs 3:5
Saul's reliance on his own plans in 1 Samuel 19:15 contradicts the advice to trust in the Lord rather than one's own understanding.
Proverbs 3:5: Trust in the LORD with all thine heart; and lean not unto thine own understanding.
Contradiction with Matthew 26:52
The intent to kill in 1 Samuel 19:15 contradicts the principle that those who use 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?