If you put it that way, even seeing is believing does not necessarily make something true because what we see we filter and interpret by means of our past beliefs, prior experiences, biases, cultural influences, and so on. In psychology, we say that believing is seeing since our beliefs so often and strongly influence what we see.
Therefore, what we are left with, whether we want it or not, is faith, which is as good as “seeing is believing” if not better. Sprinkle with a little reason and perhaps common sense, and voila, you have your religious belief.