The best way to prove God exists is by authenicity. If you are God, then you exist outside the time domain we live in because you are not restricted to time. Therefor, being not restricted to time,
you know the past, present and the future all at once. If man wrote the bible, he would fail in prophecy greatly because no one knows the future but God.
Daniel 9:25 Prophecy:
"Know therefore and understand, that from the going forth of the commandment to restore and to buld Jersualem unto the Messiah the Prince shall be seven weeks, and threescore and two weeks: the street shall be built again, and the wall, even in troublous times."
Translation: In 173,880 days after the commandment to build the temple again, the Messiah will come.
The commandment to build the temple was done by Neiamiah on March 14th 445 BC.
On april 6th, 32 AD, (173,880 days later), Jesus Christ rode a donkey into the city of Jersualem, proclaiming to be the Messiah and King of the Jews.
The margin for error of this Prophecy is ZERO.