"God is in all things by power, inasmuch as all things are subject to His power. He is in all things by presence, inasmuch as all things are naked and open to his eyes (Heb. iv, 13). He is in all things by essence, because His substance is at hand to all things as the cause of their being" (Sum. Theol., 1, q. 8, art. 3). For the scholastic meaning of 'place' see note [2.32g]. 'Space' scarcely engaged St Thomas's attention. Nor does he discuss immensity as an attribute of God. He declares: "We say that there was no place or space before the world was" (Sum. Theol., 1, q. 46, art. 1, ad 4). This is tantamount to saying that God is everywhere where creatures are; but that, apart from creation, there is no meaning in speaking of God as being everywhere.
Of God and His Creatures: 3.68