Summa Theologica, Part I (Prima Pars) From the Complete...

After considering the things belonging to the divine knowledge, we consider what belongs to the divine will. The first consideration is about the divine will itself; the second about what belongs strictly to His will; the third about what belongs to the intellect in relation to His will. About His will itself there are twelve points of inquiry:

I answer that, There is will in God, as there is intellect: since will follows upon intellect. For as natural things have actual existence by their form, so the intellect is actually intelligent by its intelligible form. Now everything has this aptitude towards its natural form, that when it has it not, it tends towards it; and when it has it, it is at rest therein. It is the same with every natural perfection, which is a natural good. This aptitude to good in things without knowledge is called natural appetite. Whence also intellectual natures have a like aptitude as apprehended through its intelligible form; so as to rest therein when possessed, and when not possessed to seek to possess it, both of which pertain to the will. Hence in every intellectual being there is will, just as in every sensible being there is animal appetite. And so there must be will in God, since there is intellect in Him. And as His intellect is His own existence, so is His will.

Reply Obj. 1: Although nothing apart from God is His end, yet He Himself is the end with respect to all things made by Him. And this by His essence, for by His essence He is good, as shown above (Q. 6, A. 3): for the end has the aspect of good.

Reply Obj. 2: Will in us belongs to the appetitive part, which, although named from appetite, has not for its only act the seeking what it does not possess; but also the loving and the delighting in what it does possess. In this respect will is said to be in God, as having always good which is its object, since, as already said, it is not distinct from His essence.

Reply Obj. 3: A will of which the principal object is a good outside itself, must be moved by another; but the object of the divine will is His goodness, which is His essence. Hence, since the will of God is His essence, it is not moved by another than itself, but by itself alone, in the same sense as understanding and willing are said to be movement. This is what Plato meant when he said that the first mover moves itself. _______________________

Obj. 4: Further, acts of will are multiplied in proportion to the number of their objects. If, therefore, God wills Himself and things apart from Himself, it follows that the act of His will is manifold, and consequently His existence, which is His will. But this is impossible. Therefore God does not will things apart from Himself.

I answer that, God wills not only Himself, but other things apart from Himself. This is clear from the comparison which we made above (A. 1). For natural things have a natural inclination not only towards their own proper good, to acquire it if not possessed, and, if possessed, to rest therein; but also to spread abroad their own good amongst others, so far as possible. Hence we see that every agent, in so far as it is perfect and in act, produces its like. It pertains, therefore, to the nature of the will to communicate as far as possible to others the good possessed; and especially does this pertain to the divine will, from which all perfection is derived in some kind of likeness. Hence, if natural things, in so far as they are perfect, communicate their good to others, much more does it appertain to the divine will to communicate by likeness its own good to others as much as possible. Thus, then, He wills both Himself to be, and other things to be; but Himself as the end, and other things as ordained to that end; inasmuch as it befits the divine goodness that other things should be partakers therein.

Reply Obj. 1: The divine will is God's own existence essentially, yet they differ in aspect, according to the different ways of understanding them and expressing them, as is clear from what has already been said (Q. 13, A. 4). For when we say that God exists, no relation to any other object is implied, as we do imply when we say that God wills. Therefore, although He is not anything apart from Himself, yet He does will things apart from Himself.

Reply Obj. 2: In things willed for the sake of the end, the whole reason for our being moved is the end, and this it is that moves the will, as most clearly appears in things willed only for the sake of the end. He who wills to take a bitter draught, in doing so wills nothing else than health; and this alone moves his will. It is different with one who takes a draught that is pleasant, which anyone may will to do, not only for the sake of health, but also for its own sake. Hence, although God wills things apart from Himself only for the sake of the end, which is His own goodness, it does not follow that anything else moves His will, except His goodness. So, as He understands things apart from Himself by understanding His own essence, so He wills things apart from Himself by willing His own goodness.

Reply Obj. 3: From the fact that His own goodness suffices the divine will, it does not follow that it wills nothing apart from itself, but rather that it wills nothing except by reason of its goodness. Thus, too, the divine intellect, though its perfection consists in its very knowledge of the divine essence, yet in that essence knows other things.

Objection 1: It seems that whatever God wills He wills necessarily. For everything eternal is necessary. But whatever God wills, He wills from eternity, for otherwise His will would be mutable. Therefore whatever He wills, He wills necessarily.