Objection 1. It would seem that corporeal creatures were produced by God through the medium of the angels. For, as all things are governed by the Divine wisdom, so by it were all things made, according to Psalm 103:24 "Thou hast made all things in wisdom." But "it belongs to wisdom to ordain," as stated in the beginning of the Metaphysics (i, 2). Hence in the government of things the lower is ruled by the higher in a certain fitting order, as Augustine says (De Trin. iii, 4). Therefore in the production of things it was ordained that the corporeal should be produced by the spiritual, as the lower by the higher.
Objection 2. Further, diversity of effects shows diversity of causes, since like always produces like. It then all creatures, both spiritual and corporeal, were produced immediately by God, there would be no diversity in creatures, for one would not be further removed from God than another. But this is clearly false; for the Philosopher says that some things are corruptible because they are far removed from God (De Gen. et Corrup. ii, text. 59).
Objection 3. Further, infinite power is not required to produce a finite effect. But every corporeal thing is finite. Therefore, it could be, and was, produced by the finite power of spiritual creatures: for in suchlike beings there is no distinction between what is and what is possible: especially as no dignity befitting a nature is denied to that nature, unless it be in punishment of a fault.
On the contrary, It is said (Genesis 1:1): "In the beginning God created heaven and earth"; by which are understood corporeal creatures. These, therefore, were produced immediately by God.
I answer that, Some have maintained that creatures proceeded from God by degrees, in such a way that the first creature proceeded from Him immediately, and in its turn produced another, and so on until the production of corporeal creatures. But this position is untenable, since the first production of corporeal creatures is by creation, by which matter itself is produced: for in the act of coming into being the imperfect must be made before the perfect: and it is impossible that anything should be created, save by God alone.
In proof whereof it must be borne in mind that the higher the cause, the more numerous the objects to which its causation extends. Now the underlying principle in things is always more universal than that which informs and restricts it; thus, being is more universal than living, living than understanding, matter than form. The more widely, then, one thing underlies others, the more directly does that thing proceed from a higher cause. Thus the thing that underlies primarily all things, belongs properly to the causality of the supreme cause. Therefore no secondary cause can produce anything, unless there is presupposed in the thing produced something that is caused by a higher cause. But creation is the production of a thing in its entire substance, nothing being presupposed either uncreated or created. Hence it remains that nothing can create except God alone, Who is the first cause. Therefore, in order to show that all bodies were created immediately by God, Moses said: "In the beginning God created heaven and earth."
Reply to Objection 1. In the production of things an order exists, but not such that one creature is created by another, for that is impossible; but rather such that by the Divine wisdom diverse grades are constituted in creatures.
Reply to Objection 2. God Himself, though one, has knowledge of many and different things without detriment to the simplicity of His nature, as has been shown above (Question 15, Article 2); so that by His wisdom He is the cause of diverse things as known by Him, even as an artificer, by apprehending diverse forms, produces diverse works of art.
Reply to Objection 3. The amount of the power of an agent is measured not only by the thing made, but also by the manner of making it; for one and the same thing is made in one way by a higher power, in another by a lower. But the production of finite things, where nothing is presupposed as existing, is the work of infinite power, and, as such, can belong to no creature.
Source: Summa Theologica (New Advent)