I saw "waiting for the call" as going to Heaven and in the process of waiting for the call, Qohen rejects food with flavor, he rejects women, it seems the life of the ascetic and his appearance (plain cloak and shaved head in a land of elaborate fashion) certainly recalls that of monks and the like. He does all this in his pursuit of faith, which at the end of the film Damon's character mocks. But then he I guess gets to go to his heaven? I'm not sure if the film is a call to faith or a mocking of it.
The whole Theorem thing, trying to prove that 0=100% (true story, back in my AP Calc class, I solved a problem ending with the answer 0=1) is the meaningless search for meaning, because there is no meaning. To the degree that we think we find meaning, it changes randomly and crumbles upon itself. And if the meaning is irrelevant and just a distraction, we might as well indulge.
His use of we vs. I seems to me his association with God/spirit...it is within him so he is plural. Attempts are made to get him to abandon that and revert to the I, attempts are made to tempt him with flesh, these could be seen as akin to the temptations of Jesus by the Devil (Damon?)