Sorry to nitpick, but the particular usage is something of a pet peeve of mine. Prophecy (long e sound at the end) is the noun (meaning both an individual prediction and the art of generating them) while prophesy (long i sound at the end) is the verb. You prophesy, uttering a prophecy.
Yeah, that’s basically how I see it too. ‘Prophesy’ is the art, ‘prophecy’ is the utterance. (I believe I mentioned that in the author’s notes back in chapter 10.)