3. The object in the first place willed is the cause of willing to every willing agent. For when we say, 'I wish to walk for the benefit of my health,' we consider that we are assigning a cause; and if we are further asked, 'Why do you wish to benefit your health?' we shall go on assigning causes until we come to the final end, which is the object willed in the first place, and is in itself the cause of all our willing. If then God wills anything else than Himself in the first place, it will follow that that 'something else' is to Him a cause of willing. But His willing is His being (Chap. LXXIII), Therefore something else will be the cause of His being, which is contrary to the notion of the First Being.
1.73 : That the Will of God is His Essence
1.75 : That God in willing Himself wills also other things besides Himself