Sometimes Christians talk about God as being pure act. While such language sounds good and wholesome, it is unlikely that even those who use the phrase know what it means. To define God as pure actuality is abstract, obscure, and strange.
And also very true.
God is pure act. If he was not, he would not be God and we would be of all people most to be pitied. For God’s promises may not be sure, his desires in process, and his goals merely a possibility.
The basic idea behind God’s pure actuality follows from God’s eternity. Since God exists eternally and so has no beginning, cause, or potentiality, then he is pure act (Thomas, Sum. Cont. Gent. 1.16). Let me try to unfold what this means.
But first, definitions
Stephen Beale explains, “something that is potential is simply something that has not yet come to be.” Beale borrows an analogy from elsewhere to illustrate his definition: “the wood of a tree is a potential table, chair, or house. Some kind of change or motion is necessary to bring the wood from a potential table to an actual table.” God does not exist in the form of divine matter that could become God. He is who he is: God.
And now, an argument
Scripture (Num 23:19; Mal 3:6; and James 1:17) and reason confirm that God cannot change. Something needed to first put the universe into motion. Scripture tells us that this something is God. But if he could change, then something put him into motion. But then God would not be before all things and so something else would share the attribute of God.
Tertullian (c. 200) engaged the philosopher Hermogenes on a similar issue. Hermogenes declared that matter and God were both eternal to save God from the charge of creating evil. Yet if something other than God shares in eternity, then this other thing shares in what God is: eternal. So matter cannot be eternal. God created it ex nihilo.
God created everything, putting it into motion. Everything created changes or ages. Anything that moves, changes, or ages exists in time for time measures change. But God does not move by changing or ageing. The psalmist affirms “you are the same, and your years have no end” (Ps 102:27).
This sameness of God entails that he does not change (Num 23:19; Mal 3:6; and James 1:17). And if he does not change, he does not move or age: “your years have no end.” But created things do change and have ends (Ps 102:25–26).
So if we return to the language of potentiality (has the ability to become or the opposite) and actuality (one who is or acts), then it becomes clear why we confess that God is pure act or actuality (I use both terms synonymously).
God lacks the ability to change, move, or age. So he cannot potentially be kind or loving. He always is. He cannot become more or less kind through habit. He is the most kind being. As a consequence, he always is and acts kindly by his unchangeably kind nature which has no beginning, middle, or end. He timelessly is Good.
He is, in this sense, pure act.
Clarifying the argument
Thomas Aquinas once wrote, “NOW if God is eternal, it follows of necessity that He is not in potentiality” (Sum. Cont. Gent. 1.16). He continued, “For everything in whose substance there is an admixture of potentiality, is possibly non-existent as regards whatever it has of potentiality, for that which may possibly be may possibly not be. Now God in Himself cannot not be, since He is eternal. Therefore in God there is no potentiality to be” (Sum. Cont. Gent. 1.16).
If legos potentially can become a house or a boat, they can be either become one thing then another thing. They have the “admixture of potentiality.” They can possibly exist one way that is possible or not.
But God doesn’t work that way. With God, “there is no variation or shadow due to change” (James 1:17). Hence, we can know for certain that God always shares of his goodness: “Every good gift and every perfect gift is from above, coming down from the Father of lights” (James 1:17). Apart from God’s pure actuality, we would not be able to affirm this reality.
If God unchangeably shares his goodness with us, his promises, his declaration of forgiveness, then he needs to be pure act. He must not change, move, or age. If we truly confess, “Of his own will he brought us forth by the word of truth, that we should be a kind of firstfruits of his creatures” (James 1:18), then we can only have assurance of this truth because his will unchangeably wills us to be his by the Word of truth.
Put more formally, the unchangeable God willed the Love of God to make us the first fruits of the new creation by the Word of God. The Father of Lights who begot the Light from all-time sent his unchangeable Love to us. Said simply, the Father sent the Son (Light) to save us by the Spirit (Love).
If God remains eternally changeless and timeless, then God is pure act. And this is the best news that we could receive. God’s promise to save us and deliver us from the wrath to come surely will come true since: “Jesus Christ [is] the same yesterday, and today, and forever” (Heb 13:8).