Imagine you declare yourself the messiah and summoned the Abrahamic God in front of every world leader. Some of them refuse to believe you so you then call out the Catholic Pope from the audience to explain it. If the Pope himself if forced to admit that you literally summoned God and are without a doubt the Messiah then how many people would be able to doubt you? It's basically the strongest double down possible since you have the highest religious authority in the world reinforcing your point.