Gal 2:7 But contrariwise, when they saw that the gospel of the uncircumcision was committed unto me, as the gospel of the circumcision was unto Peter;
Gal 2:8 (For he that wrought effectually in Peter to the apostleship of the circumcision, the same was mighty in me toward the Gentiles).
Gal 2:11 But when Peter was come to Antioch, I withstood him to the face, because he was to be blamed.
Gal 2:12 For before that certain came from James, he did eat with the Gentiles: but when they were come, he withdrew and separated himself, fearing them which were of the circumcision.
Gal 2:13 And the other Jews dissembled likewise with him; insomuch that Barnabas also was carried away with their dissimulation.
Gal 2:14 But when I saw that they walked not uprightly according to the truth of the gospel, I said unto Peter before them all, If thou, being a Jew, livest after the manner of Gentiles, and not as do the Jews, why compellest thou the Gentiles to live as do the Jews?
This was the problem with Peter, not that he abandoned the cross, and resorted to law, but he would abandon the Gentile saints, and eat with the circumcision for he feared them.
Act 10:34 Then Peter opened his mouth, and said, Of a truth I perceive that God is no respecter of persons:
Act 10:35 But in every nation he that feareth him, and worketh righteousness, is accepted with him.
Act 10:36 The word which God sent unto the children of Israel, preaching peace by Jesus Christ: (he is Lord of all).
Act 10:44 While Peter yet spake these words, the Holy Ghost fell on all them which heard the word.
Act 10:45 And they of the circumcision which believed were astonished, as many as came with Peter, because that on the Gentiles also was poured out the gift of the Holy Ghost.
Which it appears as if Peter did not understand that salvation is also for the Gentiles when he first started preaching to the circumcision, so maybe the circumcision did not understand it either.
But Peter understood salvation is for the Gentiles when Paul got in his face.