Contradiction with Matthew 5:39
Psalms 35:2 talks about taking up shield and buckler to fight, whereas Matthew 5:39 emphasizes turning the other cheek instead of fighting back.
Matthew 5:39: But I say unto you, That ye resist not evil: but whosoever shall smite thee on thy right cheek, turn to him the other also.
Contradiction with Romans 12:19
While Psalms 35:2 could be seen as a call to arms, Romans 12:19 instructs not to seek vengeance but leave it 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 14:14
Psalms 35:2 encourages actively taking up arms, whereas Exodus 14:14 suggests that the Lord will fight for you, requiring stillness rather than action.
Exodus 14:14: The LORD shall fight for you, and ye shall hold your peace.