You have that a little wrong. God *can* (in principle) be proven. If the sky breaks open, choirs of angels break forth, a 10km-long arm reaches down from the skies and an 8km golden-haired, bearded face looks down upon humanity and utters words of unshakable truth...then God is proven.
Except that isn't going to happen. If one believes the bible, at some point the believers will be vanished into heaven, which basically proves God's existence, even if he doesn't show his golden-bearded chops directly to us (which also would kill us, again, only if one believes the bible). At that point the Antichrist rises, and if we do not follow him (or her, if it is Hillary) and we choose God then we get killed. Since the obvious choice is then God is real, but the consequence for following him is death, we get a pass on our lifetime of sin and go to heaven.
Not that I actually think that is going to happen, but it made for some entertaining 1980's rapture movies. And the book of Revelation is a great read.