Objection 1. It would seem that it is not necessary that every being be created by God. For there is nothing to prevent a thing from being without that which does not belong to its essence, as a man can be found without whiteness. But the relation of the thing caused to its cause does not appear to be essential to beings, for some beings can be understood without it; therefore they can exist without it; and therefore it is possible that some beings should not be created by God.
Objection 2. Further, a thing requires an efficient cause in order to exist. Therefore whatever cannot but exist does not require an efficient cause. But no necessary thing can not exist, because whatever necessarily exists cannot but exist. Therefore as there are many necessary things in existence, it appears that not all beings are from God.
Objection 3. Further, whatever things have a cause, can be demonstrated by that cause. But in mathematics demonstration is not made by the efficient cause, as appears from the Philosopher (Metaph. iii, text 3); therefore not all beings are from God as from their efficient cause.
On the contrary, It is said (Romans 11:36): "Of Him, and by Him, and in Him are all things."
I answer that, It must be said that every being in any way existing is from God. For whatever is found in anything by participation, must be caused in it by that to which it belongs essentially, as iron becomes ignited by fire. Now it has been shown above (Question 3, Article 4) when treating of the divine simplicity that God is the essentially self-subsisting Being; and also it was shown (11, 3,4) that subsisting being must be one; as, if whiteness were self-subsisting, it would be one, since whiteness is multiplied by its recipients. Therefore all beings apart from God are not their own being, but are beings by participation. Therefore it must be that all things which are diversified by the diverse participation of being, so as to be more or less perfect, are caused by one First Being, Who possesses being most perfectly.
Hence Plato said (Parmen. xxvi) that unity must come before multitude; and Aristotle said (Metaph. ii, text 4) that whatever is greatest in being and greatest in truth, is the cause of every being and of every truth; just as whatever is the greatest in heat is the cause of all heat.
Reply to Objection 1. Though the relation to its cause is not part of the definition of a thing caused, still it follows, as a consequence, on what belongs to its essence; because from the fact that a thing has being by participation, it follows that it is caused. Hence such a being cannot be without being caused, just as man cannot be without having the faculty of laughing. But, since to be caused does not enter into the essence of being as such, therefore is it possible for us to find a being uncaused.
Reply to Objection 2. This objection has led some to say that what is necessary has no cause (Phys. viii, text 46). But this is manifestly false in the demonstrative sciences, where necessary principles are the causes of necessary conclusions. And therefore Aristotle says (Metaph. v, text 6), that there are some necessary things which have a cause of their necessity. But the reason why an efficient cause is required is not merely because the effect is not necessary, but because the effect might not be if the cause were not. For this conditional proposition is true, whether the antecedent and consequent be possible or impossible.
Reply to Objection 3. The science of mathematics treats its object as though it were something abstracted mentally, whereas it is not abstract in reality. Now, it is becoming that everything should have an efficient cause in proportion to its being. And so, although the object of mathematics has an efficient cause, still, its relation to that cause is not the reason why it is brought under the consideration of the mathematician, who therefore does not demonstrate that object from its efficient cause.
Source: Summa Theologica (New Advent)