When did the church start?

[Albion]

Indeed I believe the "great commision" given to the the church began at pentecost.

Jesus said to go out to all nations and preach the gospel and teach everyone to obey His commandments. Of course that is just waht happened starting at pentecost, when the power of the Holy Spirit descended upon them in tongues of fire and with the sound of a mighty rushing wind.

I agree...and this is the usual understanding of the question. Some people get involved with when Jesus' teachings started, others with the Hebrew scriptures' preparation for the Nativity or the OT church as forerunner to the Church of Christ, but the church is an assembly, and the commission was to go to the wider world.

It was on Pentecost that that in-gathering really got started. If we don't see this, it makes the whole episode of the Apostles cowering in the Upper Room, then the HS coming upon them, THEN Peter speaking to the multitudes (and in a miraculous way) seem unfocused or not especially significant except that some new followers joined.