Jamieson, Fausset and Brown on Galatians 2:7

7. contrariwise--on the contrary. So far from adding any new light to ME, THEY gave in THEIR adhesion to the new path on which Barnabas and I, by independent revelation, had entered. So far from censuring, they gave a hearty approval to my independent course, namely, the innovation of preaching the Gospel without circumcision to the Gentiles.

when they saw--from the effects which I showed them, were "wrought" (Ga 2:8; Ac 15:12).

was committed unto me--Greek, "I was entrusted with."

gospel of the uncircumcision--that is, of the Gentiles, who were to be converted without circumcision being required.

circumcision ... unto Peter--Peter had originally opened the door to the Gentiles (Ac 10:1-48; 15:7). But in the ultimate apportionment of the spheres of labor, the Jews were assigned to him (compare 1Pe 1:1). So Paul on the other hand wrote to the Hebrews (compare also Col 4:11), though his main work was among the Gentiles. The non-mention of Peter in the list of names, presciently through the Spirit, given in the sixteenth chapter of Romans, shows that Peter's residence at Rome, much more primacy, was then unknown. The same is palpable from the sphere here assigned to him.