This context is divided into two different passages so that first the event can be examined, and then the message Paul proclaimed (verses 14-21) can be addressed later.
When Peter came to Antioch of Syria, he and Paul had an encounter caused by Peter’s sin. Though by this time the inclusion of Gentiles into the kingdom was established (Acts 15), there was still opposition to it that Peter reacted to by “separating himself [from the Gentiles] fearing those who were of the circumcision” (12).
This was a public sin, and Paul responded publicly, admonishing Peter “before them all” (14). Peter’s actions were public, and they had led others, even Barnabas, to be “carried away with their hypocrisy” (13). Public sin can and often must be dealt with publicly. A little leaven leavens a whole lump (cf. 1 Corinthians 5:6).
Apparently, this admonition left no hard feelings, as Peter wrote approvingly of Paul in his own epistle at another time (cf. 2 Peter 3:15-16). A penitent soul does not harbor resentment for admonition.
