All things, of whatsoever kind, must be from God; for He Who is in everything by His Essence is the Cause of whatever exists by participation; and being is by participation in all except God, in Whom alone it exists by Essence; therefore all things are caused by Him.
And God is His own subsistent Being, which can be but one, as has been proved above; hence Plato says: "Before all multitude it is necessary to postulate unity"; and Aristotle: "That which is pre-eminently Being and True is the cause of all beings and of all truth." Therefore God being the Cause of all things, He is not only the Cause of their existence according to such and such accidental and substantial forms, but of all that pertains to their being, according to whatever mode they exist. Hence it is necessary to admit that even the materia prima - the first matter - has been created by the First Cause of beings.
God is also the Exemplary Cause of all things, like an artificer who conceives in his mind a determinate form which is to be carried out. For the determination of things must be reduced as its first principle to the Divine Wisdom, wherein are found the conceptions of all things, which, although multiple in respect of created things in themselves, are nevertheless no other than the Essence of God in Himself.
God is also the End of all things, because He is the First and Perfect Agent, in Whom there exists no want to be supplied; nor does He expect to acquire anything by His action, but only to communicate His perfection, which is His Goodness; this is exemplified in every creature, for every perfection is a similitude of the Perfections of God.
- text taken from Compendium of the Summa Theologica of Saint Thomas Aquinas, by Bishop Berardus Bongiovanni