Knowledge is not valid except through seeking it. It is as if the Mahdi sensed the difficulty we mentioned earlier, so he posed a question in the tongue of the seeker of guidance. He said: "Why have you obligated worship by itself, and these conditions are related to it and are not valid without them?" Then he answered by saying: "All these conditions are necessary for worship to be complete, and they are a condition for its validity and are included within it. And Our command to you for worship is Our command to you for all that is related to it and is a condition for its validity." And since the first of the conditions that he laid down for worship is faith, and since the first element of faith is faith in God, the implication of the statement is that the first obligation on a person is to know God and believe in Him, and worship is not valid except after this obligation, which is a condition for it, is fulfilled. The evidence for God's existence: Ibn Tumart followed two paths in proving God's existence, which appear contradictory on the surface, but as we will explain later, they are complementary. These are: the path of necessity and the path of inference. A. The path of necessity: The Mahdi emphasizes in various places that the Creator, may He be glorified, is known by the necessity of reason. He then explains this necessity as that which is not subject to doubt and which the rational person cannot refute. It is divided into three categories: necessary, possible, and impossible. The necessary is that which must exist, such as the dependence of an action on an actor. The possible is that which can exist and can not exist, such as the falling of rain.