D1. A proposition is either true or false.
D2. To hold to a proposition is to hold that the 1) proposition is true and to hold that 2) holding the proposition does not cause the truth of the proposition.
D3. When X is a proposition, the reason for proposition X is a proposition which is true and but for it, X would be false.
D4. When X is a proposition, the faith in a proposition X is to hold a proposition without reason.
D5. A Christian is one who has faith that God exists.
D6. An atheist is one that holds that one does not have reason to hold that God exists.

P1. It is the case that one holds that God exists or it is not the case that one holds that God exists.
P2. If it is the case that one holds that God exists, then it is the case that one has reason to hold that God exists or it is not the case that one has reason to hold that God exists.
P3. If it is the case that one holds that God exists and it is the case that one has reason to hold that God exists, then it is not the case that one has faith that God exists.
P4. If it is the case that one holds that God exists and it is the not the case that one has reason to hold that God exists, then it is the case that one has faith that God exists.

C1. Given D5 and P3, it is the case that a Christian holds that one does not have reason to hold that God exists.
C2. Given C1 and D6, both Christians and atheists hold that one does not have reason to hold that God exists.

Simplified Version

A Christian is one who has faith that God exists and because he has faith, he holds that one doesn’t have reasons to believe that God exists. Likewise, an atheists holds that one doesn’t have reasons to believe that God exists. It is somehow absurd, therefore, for a Christian to argue that one ought not be an atheist.