Why I do not believe in God

Lets take two people: Billy and Joe. Billy, who is an atheist, lived a very morally good life. He was always kind to people, donated to the homeless, etc. Joe, on the otherhand, was a very sinful man for most of his life. He assulted people, stole and even murdered someone.

Now in the last 10 years of life, Joe decided to turn his life to Christ and repent for all his sins. Billy, on the other hand, continues to lives a very morally good life until the day he dies.

Now according to Christianity, God will reward Joe with eternal paradise even though Joe did very evil things for most of his life. Meanwhile, Billy the atheist, who did nothing but brought good to the world, deserves to burn in hell for eternity.

No matter how hard I try, I just cannot bring myself to believe such a God.