What sort of thing would be enough to make an acceptable proof?
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I would think Jesus returning in some credible manner, speaking in something other than silly parables.
Parables may have worked at one time,but they are on a par with Knock Knock jokes these days.
Paul converted thousands on what turned out to be the false Second Coming.
He told people not to marry, because before the child could be born, Jesus would be back as some sort of ruler.
I do not see this happening.