A theory should not only explain what has happened, but predict what will happen. Theories about the Earth's movement in the heavens, for example, accurately predict when the sun will rise. In science, a theory must be tested using empirical means. In other words, at some point, the scientist must be able to perceive evidence for the theory with normal human senses. Only then does it become fact.
Religion is another matter.
In other words, you are supposed to believe, just because the religious view says to. The faithful will tell you, for example, that God exists in fact, in spite of the total lack of empirical evidence for God's existence. According to the religious world-view, too, all of creation exists for the benefit of man. In truth, of course, there are alternative explanations for the Earth's existence, lots of things happen for no reason, and there's no evidence that the universe exists purely for our enjoyment. For the fundamentalist who wants to believe every word of the Bible, however, life is a house of cards, with each card a tenet of faith.