The mystic approach towards life is the search for ultimate bliss. When you find bliss, you will find God too.
As the other side of the coin. Hence mysticism has no ideology of atheism or theism. It does not have any beliefs, it is simply an inquiry into truth, into the very truth of existence. Anybody can be a mystic — no belief is required.
Buddha is a mystic without any belief in God, without even a belief in the soul. If one looks from the outside, Buddha is one of the most atheistic persons who ever walked on the earth. But if one looks from within his being, then he is the greatest theist ever. That is the mystery of mysticism.