"If there is a God, He is infinitely incomprehensible, since, having, neither parts nor limits, He has no affinity to us. We are then incapable of knowing either what He is or if He is ... you must wager. It is not optional. You are embarked. Which will you choose then? Let us weigh the gain and the loss in wagering that God is. Let us estimate these two chances. If you gain, you gain all; if you lose, you lose nothing. Wager then without hesitation that he is."
The above is known as Pascal's Wager and is among the most popular arguments in support of belief in god. Personally I consider the proposition fairly dangerous since anyone following such advise is essentially bluffing god - who, if he exists, presumably knows if your faith is sincere or if you're simply hedging. To be fair Pascal did recognize this flaw, insisting believers should actually bring themselves around to honest faith, but people who try and use the Wager as an actual argument in favor of religion rarely include this corollary.
Even so, it's an eternally fascinating line of reasoning which offers no real end to academic contention. Just take a look at this link if you don't believe me:
Blaise Pascal - mathematician, physicist, religious philosopher, born June 19, 1623. If his bluff worked, he's been in Heaven for nearly 350 years now.
Happy Birthday. (Yeah, he's French...)