Interestingly, much of Pascal's writings on religion, particularly the Pensées, acknowledge the challenge posed to religious belief by the rationalism and skepticism that were part of the emergence of scientific thought. Indeed, he makes it clear that religion did not need the sanction of reason, and that reason was insufficient to understand the nature of God. He clearly thought, however, that Christianity, or at least religious belief, could survive the challenge, a position he stated most clearly in his famous "wager."
Essentially, he claimed that there are only two positions on the existence of God that one can take. Either one believes he exists, or one does not. So people had to choose, or, as Pascal puts it, to "wager." If people wagered that God did not exist, and chose not to believe, they would gain little in life if they turned out to be correct. But if they were wrong, they chose to lose everything. On the other hand, if people chose to believe in God, they would lose little if they turned out to be wrong, and if they turned out to be right, they would have gained infinitely through eternal reward. So wagering on belief, according to Pascal, is a rational decision to make. As Pascal put it, "if you gain, you gain all; if you lose, you lose nothing. Wager, therefore, that He is."