Contradiction with Matthew 5:44
Isaiah 33:12 speaks about burning and destruction of people, whereas Matthew 5:44 instructs to love enemies and do good to them.
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 12:20
Isaiah 33:12 refers to complete destruction by fire, while Romans 12:20 advises feeding and caring for enemies.
Romans 12:20: Therefore if thine enemy hunger, feed him; if he thirst, give him drink: for in so doing thou shalt heap coals of fire on his head.
Contradiction with Ezekiel 18:32
Isaiah 33:12 discusses punishment and destruction, whereas Ezekiel 18:32 states that God takes no pleasure in the death of the wicked.
Ezekiel 18:32: For I have no pleasure in the death of him that dieth, saith the Lord GOD: wherefore turn [yourselves], and live ye. [yourselves: or, others]
Contradiction with James 2:13
Isaiah 33:12 refers to people as "thorns cut up" and "burned," while James 2:13 emphasizes mercy triumphing over judgment.
James 2:13: For he shall have judgment without mercy, that hath shewed no mercy; and mercy rejoiceth against judgment. [rejoiceth: or, glorieth]