As much as I agree with the other comments that personal beliefs should be of no concern to anarchists as long as they do not impose opression and hierarchy, I would argue, however, that most religions are not in-line with anarchist thoughts because that would mean that we should ignore God's authority over people's lives.

We shouldn't exclude religious people from anarchism, of course, but I think that in the long term religious views would simply not make much sense. Most anarchists are atheists because it is a logical extension of anarchist ideas. If anarchism is the rejection of illegitimate authorities, then it follows that it is the rejection of the so-called Ultimate Authority, God. Anarchism is grounded in reason, logic, and scientific thinking, not religious thinking. Of course, not all religions have this notion of a God, so I'm not necessarily talking about them.

Indeed, as Bakunin put it in God and the State: "If God is, man is a slave; now, man can and must be free; then, God does not exist."