The first crisis of the Christian movement was not about the nature of Christ but about the terms of entry. Gentiles were joining a Jewish messianic movement in numbers, and some believers from Judaea taught that they could not be saved unless they were circumcised and kept the law of Moses. The question was not marginal. It decided whether the movement would remain a party within Judaism or become something that could absorb the empire.
The account in Acts describes a meeting of apostles and elders at Jerusalem in which Peter appealed to his own experience of gentile conversion, Paul and Barnabas reported what had happened on their journeys, and James proposed the settlement. Gentile believers would not be required to be circumcised. They were asked instead to abstain from what had been offered to idols, from blood, from meat that had been strangled and from sexual immorality, and the decision was sent out as a letter.
Two things about the outcome repay attention. The first is that the four abstentions are mostly food rules, which suggests the practical problem being solved was table fellowship between Jewish and gentile believers rather than salvation in the abstract. The second is the procedure: a dispute that could not be settled locally was referred to a wider assembly, argued, decided and circulated in writing. Every council in this atlas follows that shape, and the churches have consistently pointed back to this meeting as the reason they may hold councils at all.