When Peter... — The true reading here is undoubtedly Cephas. The visit alluded to probably took place soon after the return of Paul and Barnabas, in the interval described in Acts 15:35, shortly before the separation of these two Apostles and the departure of St. Paul on his second missionary journey.
Because he was to be blamed. — The Greek here is simply, because he was condemned. The act carried with it its own condemnation.
The blame thus imputed to St. Peter was a subject of much controversy in antiquity. It was made a ground of accusation against both Apostles. The Ebionites — as represented in the well known heretical work, the Clementine Homilies — charged St. Paul with hostility to the faith, asserting that by calling Peter “condemned” he was really accusing “God who revealed Christ in him.” On the other hand, Marcion, the Gnostic, saw in the incident a proof of the antagonism between Judaism and Christianity (as he understood it), represented by their several champions. The heathen critic Porphyry attacked both Apostles alike, the one for error, the other for forwardness in rebuking that error, and points to the whole scene as one of ecclesiastical wrangling.
The unfortunate result of these criticisms was that they led to attempts, on the part of the orthodox writers, to explain away the simple meaning of the narrative. Clement of Alexandria maintained that the Cephas here mentioned was not the Apostle St. Peter, but an inferior person, one of the seventy disciples. A more popular theory was that which was started by Origen, elaborated by Chrysostom, and defended with great vehemence by Jerome in a controversy with Augustine. This theory was that the two Apostles had arranged the scene beforehand between themselves, and acted it out for the edification of the Judaisers. St. Paul was to represent the view sanctioned by the Church, and St. Peter was to give an eminent example of submission. This view, though it held its ground for two centuries, was finally put down by the straightforwardness and good sense of St. Augustine.
The true explanation of the incident is to be found in the character of St. Peter — at once generously impulsive and timidly sensitive to the opinion of others. An inconsistency very similar to this appears in his ardent confession, followed by the betrayal of his Master (Mark 14:29; Mark 14:66 et seq.). It had been seen at an earlier date in his attempt to walk upon the water (Matthew 14:28-33); and is, indeed, one of the features in his character most conspicuous in the Gospels. A little more attention to this would have saved many doctrinaire objections to the narrative of the Acts, where the inconsistency, which is really one of character, is treated as if it stood in the way of the objective truth of the events.