Saadia is a philosopher who stands in the jewish tradition of philosophy. Saadia originally came from Egypt and was the first to practice systematic philosophy in judaism. His main interests were physics, metaphysics, logic, ethics and politics. Under Saadia, Hebrew became more important as a philosophical language. Religion was important for him, but Saadia managed to combine science with religion (mainly the science of philosophy). He kept defending theism and said that both reason and revelation led to proper knowledge. His main contribution to philosophy was the systematization of the jewish thought, his philosophical reflection on religious matters. He went beyond rabbinical and Talmudic theology, and managed to combine philosophy and judaism.
In my opinion, the way Saadia combined his belief with his religion is very similar to what other philosophers did with their religions. They all keep believing what they always believed, and find a way to bring philosophy into it. I do see that by introducing philosophy into a religion, people start thinking instead of just believing and doing what their religion says. This is, in my opinion, a good thing, because just believing something and acting according to that can be quite dangerous. I think what Saadia did here may have been the start of the very slow movement of people becoming atheist. But again, this is a movement started by the entire tradition of medieval philosophers, since almost all of them started bringing philosophy and religion together.
Medieval Philosophy Blog 