Blaise Pascal (1623-1662) was a world famous French Mathematician, as well as a great Christian thinker. His contributions to the field of geometry in particular are well known today. Pascal developed many arguments in favor of the existence of God. Therefore he proposed what has come to be known as Pascal's Wager. This is a common sense analysis of the benefits and consequences of belief or unbelief in the existence of GOD.
If God does not exist, and we wager that he does (by believing), then we lose nothing, since, presumably, there is no afterlife or eternal reward or punishment for belief or unbelief.
If God does exist, however, and offers us the free gift of eternal life, and we wager that he does not (by unbelief), then we risk losing everything by spending eternity separated from God.
If God does exist, and we wager that he does, then we potentially gain eternal life and happiness.
So, said Pascal, a reasonable person who even considers the possibility that God exists to be about 50-50 should wager that he does, since that person stands to lose nothing and gain everything, whereas the person who wagers that God does not exist stands to gain nothing (if God does not exist), or lose everything (if God does exist).
It should be noted that Pascal also held that the possibility of God's existence was much greater than 50-50.
While this is not a proof for God's existence, it does demonstrate the seriousness of the consequences of either belief or unbelief which a reasonable person ought to carefully consider.