Divine simplicity means that, just as God does not depend on anything outside himself, so in himself he does not have any parts he depends on in order to be who he is. In other words, God does not derive his being from any quality or idea or thing that might pre-exist him.
One of the key moments of God’s self-revelation in Scripture happens at the burning bush, when Moses asks God, “What is your name?” God answers, “I am who I am” (Exodus 3:14).
Here we see that God does not receive his name, identity, or existence from anyone or anything else. He does not depend on anything to be who he is. He simply and eternally is. It is a truth picked up many times in Scripture, for example in John’s Gospel, where we see that the Word (who again calls himself “I am,” John 8:48) does not acquire life but has “life in himself” (John 5:26).
This is why Paul can tell the Athenians, “The God who made the world and everything in it, being Lord of heaven and earth, does not live in temples made by man, nor is he served by human hands, as though he needed anything” (Acts 17:24–25). The living God isn’t in any need. He doesn’t need anything to be better, to be more God, or to be more fully himself. He depends on nothing. He has fullness of being. He has life in himself.
Theologians call this the doctrine of God’s self-existence or aseity (from the Latin a se, meaning “from/of himself”). From this characteristic of God, we will see, flows all the graciousness of the gospel.
God Needs Nothing
In this lack of need, God is utterly different from idols.
In Acts 19, in Ephesus, Demetrius the idol-maker makes a striking admission. He complains that if Paul is allowed to say that man-made gods are no gods at all, then
…there is danger not only that this trade of ours may come into disrepute but also that the temple of the great goddess Artemis may be counted as nothing, and that she may even be deposed from her magnificence, she whom all Asia and the world worship. (Acts 19:27)
In other words, the divine majesty of Artemis is dependent on the service of her worshipers. For all her apparent magnificence, she needs her minions. In herself she is empty and parasitic.
In absolute contrast, God does not need the world in order to satisfy himself or to be himself. The divine majesty of God is not dependent on the world. God did not create the world because of any lack in himself. He created because he was so happily self-existent, so bursting with benevolence. God is so overflowingly, superabundantly full of life in himself that he delighted to spread his goodness.
Because of God’s blessed aseity, we can know that the very creation is a work of grace. Grace, then, is not merely his kindness to those who have sinned. Before there was sin, God brought creation into being out of grace. With the self-existent God, love is not a reaction. God’s love is creative. He gives life and being as a free gift, for his very life, being, and goodness are yeasty, spreading out that there might be more that is truly good.
Where idols need worship and service and sustenance, God needs nothing. He has life in himself — and so much so that he is brimming over. His glory is overflowing, radiant, and self-giving. Because God is self-existent and does not need us, he relates to us by sheer grace. No other god can do that.