The orbiting teapot

I'm parsing a statement that recently came across my desk (so to speak):

I have religious duties to perform at my church. I cannot say for sure that God exists, but if he does exist, he wants me to be doing these things.

Whatever the content might be, it has to reside in that final indicative, "He wants me to be doing these things [i.e., performing my religious duties at church]."
    The question of course is, how does the speaker know what God, "if he does exist," wants him to be doing? How can he know that if he doesn't even know whether God exists?

My dear Watson! In a trivial sense, it's elementary. He knows because his conception of the God that might exist is of a God who wants him to be doing those very duties. That is, the speaker's statement, "unpacked"—as Professor Wildrid Sellars liked to say—amounts to this:

If God (defined as a being who, if he existed, would want me to perform these religious duties) exists, then he wants me to be doing these things.

It's as if I were to say (to use Bertrand Russell's famous example¹):

If an undetectably small china teapot were revolving about the sun, I know that it would be undetectably small.

Among other things, this sort of statement is called a tautology. The predicate doesn't add anything not already contained in the subject. If you assume that God exists, then (in your world) God exists, and he wants you to be doing whatever you specify that he wants you to be doing.
    Welcome to your world!
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1. Wikipedia conveniently quotes the passage from Russell in which the teapot is specified:

   In an article entitled "Is There a God?" commissioned, but never published, by Illustrated magazine in 1952, Russell wrote:
       If I were to suggest that between the Earth and Mars there is a china teapot revolving about the sun in an elliptical orbit, nobody would be able to disprove my assertion provided I were careful to add that the teapot is too small to be revealed even by our most powerful telescopes. But if I were to go on to say that, since my assertion cannot be disproved, it is an intolerable presumption on the part of human reason to doubt it, I should rightly be thought to be talking nonsense. If, however, the existence of such a teapot were affirmed in ancient books, taught as the sacred truth every Sunday, and instilled into the minds of children at school, hesitation to believe in its existence would become a mark of eccentricity and entitle the doubter to the attentions of the psychiatrist in an enlightened age or of the Inquisitor in an earlier time. [emphasis mine]