In “Judaism, the Circumcision of Gentiles, and Apocalyptic Hope: Another Look at Galatians 1 and 2” (JTS 42 (1991): 532-64), Paula Fredriksen distinguishes between inclusion and conversion of Gentiles. The early inclusion of Gentiles cohered with apocalyptic belief; the later controversy over their conversion owed to the delayed apocalypse. Fredriksen writes:
“From its inception, the Christian movement admitted Gentiles without demanding that they be circumised and observe the Law…until 49 CE, evidently… What had changed between c. 30 and c. 49 CE, and why? Posing the question puts the answer…The kingdom did not come. Time drags when you expect it to end. Put differently, millenarian movements tend, of necessity, to have a short half-life. As the endtime recedes, reinterpretations and adjustments must reshape the original belief, else it be relinquished to unintelligibility or irrelevance.” (pp 558-559)
We thus have an irony. In the earliest days of apocalyptic fervor, Gentiles were (naturally) admitted into the Christian movement as Gentiles, without needing to become proselyetes. This is probably what Paul refers to in Gal 5:11: the period before his conversion when he zealously urged circumcision on these pagans who were sharing indiscriminate eucharist fellowship with Jews. After his conversion he not only accepted Gentiles as the other apostles did, but he saw them as his prime mission, and began evangelizing abroad.
But twenty years is a long delay for the kingdom — and a long time to be fending off persecutions from wider Judaism. The success of Paul’s large-scale mission would have made the issue more poignant: Can Gentiles really go on being included as implied equals without converting? The apostles had increased misgivings and knew they had to evolve accordingly. Paul, on the other hand, wasn’t about to relinquish this aspect of the millenial dream: the Gentiles were his babies.
Paul began as a foe of Christianity, and of Gentiles in particular. The other apostles began as apocalyptic enthusiasts, welcoming Gentiles as they were. Yet Paul ended up championing the pagans uncompromisingly, while the pillars ended up imposing conversion requirements — and circumcision, no less — in act of treachery and revenge.