This is a classic apologetic from the great 17th century French mathematician, physicist and philosopher, Blaise Pascal:

1. If God does not exist, and I believe that He exists—I lose nothing.
(Christian)

2. If God does not exist, and I don’t believe that He exists—I lose nothing. (Atheist)

3. If God exists, and I believe that He exists—I gain everything.
(Christian)

4. If God exists, and I don’t believe that He exists— I lose everything. (Atheist)
Essentially, Pascal is asking the reader, “Within the context of eternity, which is the safest of the following propositions?” The only winning position is #3.
—From William J. Tsamis, apologetics.org

Who is Blaise Pascal and what is this Wager all about?
Pascal’s Wager – Blaise Pascal (1623-62) was a famous French mathematician, physicist, and philosopher who truly sought to understand the meaning of his existence in this vast universe. Like any man of intellect, Pascal struggled with the concept of God’s existence, saying, “I see too much to deny God, yet too little to be sure.” Essentially, what he meant was that he saw the evidence of God’s existence in the glory of creation, yet at the same time he perceived certain difficulties as well, such as the problem of evil. After years of contemplation, however, Pascal decided to become a Christian and follow the path of the Savior. His philosophical work, Pensees (Lit. “thoughts”), is one of the classic spiritual writings of all time. Anyway, for those suspended in agnosticism, Pascal devised the following formula, called Pascal’s Wager, because ultimately it demands that one gamble (wager) his existence on one of the following propositions:

Photo from http://www.philosophyprofessor.com/philosophers/blaise-pascal.php