Christians cannot prove the existence of the God they believe exists. By reason, we cannot defend either the proposition that God exists or that He does bot exist. Whoever bets that God is, takes the least risk. For if we bet that exists and it turns out that He does not exist, we have lost nothing. But if we bet that He does not exist and it turns out that He does, we have lost everything in terms of happiness, the end of life.
The argument as stated is slightly flawed. First, there is a cost in becoming a Christian, for Christ must come first in ones life. Second, he does not consider other religions (I will do this later). However, the core of the argument is sound: Christianity offers unspeakable riches: eternal life. Atheism, on the other hand, promises nothing after death. So if you are to reject Christianity, you had better be sure that you are right. So just remember...
...What if you are wrong?