The beginning of Gospel proclamation was not eye-witnesses trying to convince those who had not seen, but one group of eye-witnesses seeking to help other eye-witnesses understand what they all had seen. Even as Gospel proclamation continued on it was grounded in events that had happened and been seen and experienced.
From Dale Ralph Davis:
What does one make of all that? These were things that the early preachers of the gospel said and preached as eyewitnesses, as men who had been there. Here’s the crucial point: when they were preaching these things, they were preaching to other eyewitnesses, and they were often preaching to a lot of hostile eyewitnesses. If what the preachers were saying was not true, those hostile eyewitnesses would have exposed it as a fraud in the first century and you would never have heard of Christianity. Why didn’t that happen? Because even the hostile hearers could not dispute the truth and accuracy of what these original evangelists were proclaiming. When you preach in front of hostile hearers, you have to be careful with your facts. So, if you resist the gospel, do not claim that there is not enough evidence. There is evidence for you to deal with.
Dale Ralph Davis, True Words For Tough Times, EP Books, 2013, pg 69.