I answer that, God is said to be in a thing in two ways; in one way after the manner of an efficient cause; and thus He is in all things created by Him; in another way he is in things as the object of operation is in the operator; and this is proper to the operations of the soul, according as the thing known is in the one who knows; and the thing desired in the one desiring. In this second way God is especially in the rational creature which knows and loves Him actually or habitually. And because the rational creature possesses this prerogative by grace, as will be shown later (Q. 12). He is said to be thus in the saints by grace.
But how He is in other things created by Him, may be considered from human affairs. A king, for example, is said to be in the whole kingdom by his power, although he is not everywhere present. Again a thing is said to be by its presence in other things which are subject to its inspection; as things in a house are said to be present to anyone, who nevertheless may not be in substance in every part of the house. Lastly, a thing is said to be by way of substance or essence in that place in which its substance may be. Now there were some (the Manichees) who said that spiritual and incorporeal things were subject to the divine power; but that visible and corporeal things were subject to the power of a contrary principle. Therefore against these it is necessary to say that God is in all things by His power.
But others, though they believed that all things were subject to the divine power, still did not allow that divine providence extended to these inferior bodies, and in the person of these it is said, "He walketh about the poles of the heavens; and He doth not consider our things [*Vulg.: 'He doth not consider . . . and He walketh,' etc.]" (Job 22:14). Against these it is necessary to say that God is in all things by His presence.
Further, others said that, although all things are subject to God's providence, still all things are not immediately created by God; but that He immediately created the first creatures, and these created the others. Against these it is necessary to say that He is in all things by His essence.
Therefore, God is in all things by His power, inasmuch as all things are subject to His power; He is by His presence in all things, as all things are bare and open to His eyes; He is in all things by His essence, inasmuch as He is present to all as the cause of their being.
Reply Obj. 1: God is said to be in all things by essence, not indeed by the essence of the things themselves, as if He were of their essence; but by His own essence; because His substance is present to all things as the cause of their being.
Reply Obj. 2: A thing can be said to be present to another, when in its sight, though the thing may be distant in substance, as was shown in this article; and therefore two modes of presence are necessary; viz. by essence and by presence.
Reply Obj. 3: Knowledge and will require that the thing known should be in the one who knows, and the thing willed in the one who wills. Hence by knowledge and will things are more truly in God than God in things. But power is the principle of acting on another; hence by power the agent is related and applied to an external thing; thus by power an agent may be said to be present to another.
Reply Obj. 4: No other perfection, except grace, added to substance, renders God present in anything as the object known and loved; therefore only grace constitutes a special mode of God's existence in things. There is, however, another special mode of God's existence in man by union, which will be treated of in its own place (Part III). _______________________
FOURTH ARTICLE [I, Q. 8, Art. 4]