Some people believe there is a God.  Personally I don't but I certainly can't prove there isn't - in fact to be fair the existence of a God would explain an awful lot.

The belief in a God is a matter of faith - once the existence of a God is accepted though then it is reasonable that this God would want to communicate with us and the use of an envoy or 'prophet' seems perfectly reasonable - it is of course a matter of faith when deciding which is the true 'word of God' and which are false prophets.

It is at this point things become difficult - once you have faith that an individual is speaking the Word or that a book is the Word of God then you can't doubt that Word without doubting the existence of God.

No one can prove that Creationism is wrong and that the Universe isn't just 6,000 or whatever years old - sure you can carbon date fossils and show they are millions of years old but God may have made them like that!