III. There is a still deeper and more exhaustive conception of the Divine Substance contained in the expressions, “God is His own existence;” “God’s essence is existence;” “God is Being;” ὁ ὤν, He Who is, Jehovah. The Schoolmen express this by saying, “God is a pure act (actus purus);” that is, pure actuality without any admixture of potentiality. Every perfection possible in any being is actually possessed by God, and is only possible in others because it actually exists in Him. The name Jehovah, understood in this sense, is really the essential name of God. This Divine Actuality is the foundation of God’s Simplicity and Infinity. His Simplicity consists in the identity of possibility and reality, and His Infinity means that every possible perfection is actually possessed by Him.

Joseph Wilhelm and Thomas B. Scannell, A Manual of Catholic Theology: Based on Scheeben’s “Dogmatik,” Fourth Edition, Revised. (London; New York; Cincinnati; Chicago: Kegan Paul, Trench, Trübner & Co., Ltd.; Benziger Bros., 1909), 176.

The passage from Wilhelm and Scannell’s Manual of Catholic Theology (a summary of Scheeben) presents one of the most profound affirmations in classical Christian theology: God is not merely a being who exists; He is existence itself, pure actuality without any trace of potentiality. This conception, rooted in the divine name revealed at the burning bush, grounds both God’s absolute simplicity and His infinity. It is a careful reflection on Scripture’s self-revelation of God as the One who simply is, in a way no creature ever can.

The Divine Name: “He Who Is”

Scripture discloses God’s essential name in Exodus 3:14. When Moses asks what he shall say to the Israelites, God answers, “I AM WHO I AM” (אֶהְיֶה אֲשֶׁר אֶהְיֶה, ʾehyeh ʾăšer ʾehyeh), and then instructs, “Say this to the people of Israel: ‘I AM has sent me to you.’” The following verse gives the name by which God is to be remembered forever: YHWH (יהוה), commonly rendered “the LORD” but linked etymologically to the verb hayah (“to be”).

The Hebrew construction ʾehyeh ʾăšer ʾehyeh is deliberately emphatic. It refuses definition by anything outside God Himself. God does not say “I am [something]”; He declares existence as His ownmost reality. The Septuagint translates this as ἐγώ εἰμι ὁ ὤν (“I am the One Who Is”), and the Vulgate follows with ego sum qui sum (“I am who am”). Early interpreters, including Augustine and Thomas Aquinas, saw here the revelation of God as subsistent being itself ipsum esse subsistens. God does not participate in being; He is being, the font from which all finite existence flows. Isaiah echoes the same truth when God declares, “I am the first and I am the last; besides me there is no god” (Isa 44:6). Revelation 1:8 places the same self-designation from the risen Lord who said, “I am the Alpha and the Omega . . . who is and who was and who is to come, the Almighty.” The One who eternally is confronts time-bound creatures with His unchanging reality.

God as Pure Act (Actus Purus)

The Schoolmen, above all Thomas Aquinas, express this scriptural truth metaphysically: God is actus purus meaning that God is pure act, pure actuality, without any admixture of potentiality. In creatures, everything is a mixture. We possess potentiality: we can become wiser, stronger, holier, or the opposite. We move from potency to act through change, receiving perfections we did not previously possess. Potentiality implies imperfection, dependency, and capacity for change. But God, as the first cause and necessary being, cannot depend on anything or undergo change. If He could move from potency to act, something would actualize Him, and He would not be first.

Thomas argues this rigorously in the Summa Theologiae. Since actuality precedes potentiality absolutely (for only what is actual can reduce potency to act), and God is the first being, it is impossible that in God there should be any potentiality (ST I, q. 3, a. 1). God is therefore pure act: every perfection possible in any being exists in Him actually and infinitely. Whatever goodness, wisdom, power, or beauty appears in creatures exists only because it first exists eminently in God. As Aquinas puts it, God is not good because He participates in goodness; goodness exists because He is goodness itself (ST I, q. 6). God declares, “I the LORD do not change” (Mal 3:6). James affirms, “Every good gift and every perfect gift is from above, coming down from the Father of lights, with whom there is no variation or shadow due to change” (Jas 1:17). The psalmist cries, “Of old you laid the foundation of the earth, and the heavens are the work of your hands. They will perish, but you will remain; they will all wear out like a garment . . . but you are the same, and your years have no end” (Ps 102:25–27). God’s unchanging fullness of being undergirds creation’s mutability.

Simplicity and Infinity Grounded in Divine Actuality

This pure actuality is the foundation of two cardinal attributes.

First, simplicity. Because God is pure act, there is no composition in Him and no distinction between essence and existence, between substance and accidents, between possibility and reality. In creatures, essence (what a thing is) differs from existence (that it is); we exist by participation. In God, essence and existence are identical: God is His own existence. His attributes are not added qualities; they are identical with His being. He is not wise by participating in wisdom; He is wisdom. As Thomas explains, “in God . . . essence and existence are the same” (ST I, q. 3, a. 4).

Second, infinity. Because God is pure act without potentiality, He possesses every possible perfection actually and without limit. Infinity here is not mere extension but intensive plenitude: God exhausts all that being can be. Creatures are finite because they receive limited perfections; God is infinite because He is all perfections in sovereign unity. “Great is the LORD, and greatly to be praised, and his greatness is unsearchable” (Ps 145:3).

Herman Bavinck echoes this scriptural and patristic doctrine arguing that God is simple, free from all composition, so that His attributes are identical with His being; He is pure essence, possessing all perfections simultaneously and completely.

Conclusion: Worship and Wonder

The quote invites us to adoration. The God who spoke ʾehyeh ʾăšer ʾehyeh at the bush is the One whose being grounds every breath we take. Because He is pure act, we need not fear that His perfections could fail or diminish. Because He is simple and infinite, His love, justice, and mercy are not competing parts but one undivided reality poured out in Christ.

We are contingent; He is necessary. We become; He simply is. Yet in astonishing grace, the I AM has drawn near, taken flesh, and said, “Before Abraham was, I am” (John 8:58). In Him we behold the fullness of being and find our being renewed.