"I get e-mails from Christians on a regular basis. Many of them are convinced that the Holy Spirit has instructed them to contact me and give me valuable evidence that will change my mind. These people believe that their god is real, that he wants me to know that he's real and that he's charged them with providing me with the evidence.
We can, via reducto ad absurdum, demonstrate that these people are simply wrong:
If their god exists, then it knows precisely what information they'll need to convey to convince me and it would communicate this information to a person who is capable of accurately presenting it in a way that achieves the stated goal. (I'm not going to draw out a syllogism for this...it's all from the definition of the god that they believe is real.)
Why then do these people consistently present the most obviously flawed arguments and absurd anecdotal evidence? Why then do these people often say the very thing that *confirms* that they have no clue what they're talking about?
Are they just inept at communicating the needed information? Then their god has made a terribly stupid mistake, inconsistent with the character of the god they believe in.
Is their god incapable of accurate communication? Not according to their beliefs. Their god is perfectly (or nearly) wise, intelligent, capable, powerful, etc...and clearly directed them to present the information.
No matter how you break this down, the god they believe in simply doesn't exist. There may be a god, and it might even be the one that they're trying to represent, but they're clearly wrong about its desire and ability to demonstrate its existence. At best we're left with something that is, to a third party, indistinguishable from delusion."