Objection 1. It would seem that God cannot move the matter immediately to receive the form. For as the Philosopher proves (Metaph. vii, Did. vi, 8), nothing can bring a form into any particular matter, except that form which is in matter; because, like begets like. But God is not a form in matter. Therefore He cannot cause a form in matter.
Objection 2. Further, any agent inclined to several effects will produce none of them, unless it is determined to a particular one by some other cause; for, as the Philosopher says (De Anima iii, 11), a general assertion does not move the mind, except by means of some particular apprehension. But the Divine power is the universal cause of all things. Therefore it cannot produce any particular form, except by means of a particular agent.
Objection 3. As universal being depends on the first universal cause, so determinate being depends on determinate particular causes; as we have seen above (Question 104, Article 2). But the determinate being of a particular thing is from its own form. Therefore the forms of things are produced by God, only by means of particular causes.
On the contrary, It is written (Genesis 2:7): "God formed man of the slime of the earth."
I answer that, God can move matter immediately to form; because whatever is in passive potentiality can be reduced to act by the active power which extends over that potentiality. Therefore, since the Divine power extends over matter, as produced by God, it can be reduced to act by the Divine power: and this is what is meant by matter being moved to a form; for a form is nothing else but the act of matter.
Reply to Objection 1. An effect is assimilated to the active cause in two ways.
First, according to the same species; as man is generated by man, and fire by fire.
Secondly, by being virtually contained in the cause; as the form of the effect is virtually contained in its cause: thus animals produced by putrefaction, and plants, and minerals are like the sun and stars, by whose power they are produced. In this way the effect is like its active cause as regards all that over which the power of that cause extends. Now the power of God extends to both matter and form; as we have said above (14, 2; 44, 2); wherefore if a composite thing be produced, it is likened to God by way of a virtual inclusion; or it is likened to the composite generator by a likeness of species. Therefore just as the composite generator can move matter to a form by generating a composite thing like itself; so also can God. But no other form not existing in matter can do this; because the power of no other separate substance extends over matter. Hence angels and demons operate on visible matter; not by imprinting forms in matter, but by making use of corporeal seeds.
Reply to Objection 2. This argument would hold if God were to act of natural necessity. But since He acts by His will and intellect, which knows the particular and not only the universal natures of all forms, it follows that He can determinately imprint this or that form on matter.
Reply to Objection 3. The fact that secondary causes are ordered to determinate effects is due to God; wherefore since God ordains other causes to certain effects He can also produce certain effects by Himself without any other cause.
Source: Summa Theologica (New Advent)