Contradiction with Matthew 15:24
Jesus states he was sent only to the lost sheep of Israel, whereas Isaiah 42:6 speaks of being a light to the Gentiles.
Matthew 15:24: But he answered and said, I am not sent but unto the lost sheep of the house of Israel.
Contradiction with Acts 13:46
Paul and Barnabas declare turning to the Gentiles as a reaction to Jewish rejection, but Isaiah 42:6 presents the call to the Gentiles as an original mission.
Acts 13:46: Then Paul and Barnabas waxed bold, and said, It was necessary that the word of God should first have been spoken to you: but seeing ye put it from you, and judge yourselves unworthy of everlasting life, lo, we turn to the Gentiles.
Contradiction with Romans 15:8
States Jesus was a minister of the circumcision for the truth of God, focusing on the Jews, which seems to contradict the broader mission expressed in Isaiah 42:6.
Romans 15:8: Now I say that Jesus Christ was a minister of the circumcision for the truth of God, to confirm the promises [made] unto the fathers: