A.T. Robertson Commentary Galatians 2:8

"(for he that wrought for Peter unto the apostleship of the circumcision wrought for me also unto the Gentiles);" — Galatians 2:8 (ASV)

He that wrought for Peter unto the apostleship of the circumcision (ο γαρ ενεργησας Πετρω εις αποστολην της περιτομης). Paul here definitely recognizes Peter's leadership (apostleship, αποστολην, late word, already in Ac 1:25; 1 Corinthians 9:2) to the Jews and asserts that Peter acknowledges his apostleship to the Gentiles. This is a complete answer to the Judaizers who denied the genuineness of Paul's apostleship because he was not one of the twelve.