Pascal spent the final years of his life putting together the beginnings of an apologia for Christianity. Although it was never fully completed, the extant material was pieced together and published. It is in this work that one finds Pascal's famous wager.
The argument is as follows: either God exists or he does not. We have to choose one way or the other on this issue; it is an unavoidable existential dilemma. If God does not exist , then we lose very little by believing that he does exist. If he does exist, then we stand to gain an awful lot by believing that he does , and to lose an awful lot by thinking that he doesn't.
The wager is not an argument for the existence of God; Pascal was aware that he could not convince unbelievers of God's existence by rational argument.
It is seen as an early example of decision-theory. Pascal's reach was broad , and in the modern era his scientific and mathematical work is perhaps more impressive than his religious apologetics.
Watch this video
You don't want an existential crisis