It consists of three parts Part I treats of God who is the first cause himself

It consists of three parts. Part I treats of God, who is the " first cause , himself uncaused" ( primum movens immobile ) and as such existent only in act ( actu ), that is pure actuality without potentiality and, therefore, without corporeality. His essence is actus purus et perfectos . This follows from the fivefold proof for the existence of God; namely, there must be a first mover, unmoved, a first cause in the chain of causes, an absolutely necessary being, an absolutely perfect being, and a rational designer. In this connection the thoughts of the unity, infinity , unchangeableness, and goodness of the highest being are deduced. The spiritual being of God is further defined as thinking and willing. His knowledge is absolutely perfect since he knows himself and all things as appointed by him. Since every knowing being strives after the thing known as end, will is implied in knowing. Inasmuch as God knows himself as the perfect good, he wills himself as end. But in that everything is willed by God, everything is brought by the divine will to himself in the relation of means to end. Therein God wills good to every being which exists, that is he loves it; and, therefore, love is the fundamental relation of God to the world. If the divine love be thought of simply as act of will, it exists for every creature in like measure: but if the good assured by love to the individual be thought of, it exists for different beings in various degrees. In so far as the loving God gives to every being what it needs in relation to the whole, he is just: in so far as he thereby does away with misery, he is merciful. In every work of God both justice and mercy are united and, indeed, his justice always presupposes his mercy, since he owes no one anything and gives more bountifully than is due. As God rules in the world, the "plan of the order of things" preexists in him; i.e., his providence and the exercise of it in his government are what condition as cause everything which comes to pass in the world. Hence follows predestination : from eternity some are destined to eternal life, while as concerns others "he permits some to fall short of that end". Reprobation, however, is more than mere foreknowledge; it is the "will of permitting anyone to fall into sin and incur the penalty of condemnation for sin". The effect of predestination is grace. Since God is the first cause of everything, he is the cause of even the free acts of men through predestination. Determinism is deeply grounded in the system of Aquinas; things with their source of becoming in God are ordered from eternity as means for the realization of his end in himself. On moral grounds Aquinas advocates freedom