No one would believe it, until "He" demonstrated His mighty and benevolent power. Then most people would fear, certainly question this being, though many would begin to worship.
As more and more people began accepting His intervention, the established powers that be (eg, national governments), would begin to see Him as a potential threat. Top secret organizations would form to study this being (dominant hypothesis: advanced alien), and try to discover weaknesses. There may well be (probing?) attacks launched.
Some religions (and atheists) will adapt better than others; it will be a momentous time for flexible thinking. In time, like people, nations will either adapt and accept, or go down in revolution and flame, then to be reborn. In time, and only in time, will the world as a whole accept the truth.
In the far future, after much diminishing grief and expanding joy, this presence will awaken all over, for an infinite, eternal moment, then, smiling, will begin the Dream anew.
😎