I think the birth would really strike and touch some people that were present, but will not be believed or known about by many out of that circle. Much as what happened so many years ago.
But I do not think that the man would only be a passing act. He moved a lot of people at the time, strongly enough to change their religion, to die for this religion and to pass it to others with conviction enough to grow in numbers and strength enough to make the roman emperor take it, instead of opposing it any further. From prosecution and hiding, to centre stage.
It must have been the strongest of faiths that moved all this peole. I would love to know more about the early christians. I think once Rome adopted the religion, they added quite a few bits and, well, started using it to control others. I would love to know on its pure form, the way to be the best human we can be.