I believe that is called Pascals Wager. It essentially states that not believing in god is a bad bet.
* You live as though God exists.
o If God exists, you go to heaven: your gain is infinite.
o If God does not exist, you gain nothing & lose nothing.
* You live as though God does not exist.
o If God exists, you go to hell: your loss is infinite.
o If God does not exist, you gain nothing & lose nothing.
I like this quote better though.
Suppose there is a God who is watching us and choosing which souls of the deceased to bring to heaven, and this god really does want only the morally good to populate heaven. He will probably select from only those who made a significant and responsible effort to discover the truth. For all others are untrustworthy, being cognitively or morally inferior, or both. They will also be less likely ever to discover and commit to true beliefs about right and wrong. That is, if they have a significant and trustworthy concern for doing right and avoiding wrong, it follows necessarily that they must have a significant and trustworthy concern for knowing right and wrong. Since this knowledge requires knowledge about many fundamental facts of the universe (such as whether there is a god), it follows necessarily that such people must have a significant and trustworthy concern for always seeking out, testing, and confirming that their beliefs about such things are probably correct. Therefore, only such people can be sufficiently moral and trustworthy to deserve a place in heaven — unless god wishes to fill heaven with the morally lazy, irresponsible, or untrustworthy.
—Richard Carrier, The End of Pascal's Wager: Only Nontheists Go to Heaven
