(Before It's News)
Pascal’s Wager is an argument in apologetic philosophy which was devised by the seventeenth-century French mathematician, physicist, and philosopher Blaise Pascal (1623–1662). It posits that humans all bet with their lives either that God exists or does not exist. Given the possibility that God actually does exist and assuming the infinite gain or loss associated with belief in God or with unbelief, a rational person should live as though God exists and seek to believe in God. If God does not actually exist, such a person will have only a finite loss (some pleasures, luxury, etc.).
The philosophy uses the following logic:
1. God is, or He is not.
2. A Game is being played where heads or tails will turn up.
3. According to reason, you can defend neither of the propositions.
4. You must wager. (It’s not optional.)
5. 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.
Historically, Pascal’s Wager was groundbreaking because it charted new territory in probability theory, marked the first formal use of decision theory, and anticipated future philosophies such as existentialism, pragmatism, and voluntarism.

Source:
http://www.ascensionearth2012.org/2014/08/pascals-17th-century-wager-god-is-or-he.html