The Jesus Seminar is evidently still at it. On the Crosstalk mailing list, Gordon Raynal mentions the group’s upcoming agenda.
“In the next year the group wants to assess the arguments for and against the following statements:
1. Christianity began with Pentecost.
2. Christianity began with the Resurrection.
3. Christianity began with Jesus.
4. Christianity began with Paul.”
There should be another option acknowledging Acts 11:26, where Luke reports that “in Antioch the disciples were first called Christians.”
People have been tackling this question forever, and the answer naturally depends on what is meant by the term “Christianity”. If by it we mean simply a sectarian group, then I actually have no problems saying that Christianity began with Jesus himself. But for historical purposes I’m inclined to take the ancient perceptions of this matter more seriously, such as the tradition preserved in Acts 11:26. By this time (mid-40s? a decade or two after Jesus?) the sectarian nature of the movement was evidently extending into territory radical enough to call forth a new label. It was probably mixed table-fellowship with uncircumcised Gentiles (a practice predating Paul, in my view, perhaps the reason for which he persecuted the sect so mercilessly) which precipitated the special name: christianoí. Christianity essentially began with Jesus, but more officially began years later with unidentified followers who began incorporating the Gentile peoples in a manner for which Paul would become renowned as the originator.