How did Aquinas explain the difference between God and created beings?

In the context of Scholasticism, St. Thomas Aquinas explained the fundamental difference between God and created beings through the metaphysical distinction between essence and existence.12

Aquinas conceived of being as the act of existing (esse). He posited that God is "pure being," meaning that in God, essence and existence are identical—God’s essence is his existence.123

In contrast, all created beings are finite and possess a real composition of essence and existence. Creatures do not possess existence in their own right; rather, they participate in being according to the limitations of their specific essence. For example, a human being participates in the act of existing only to the extent that their humanity permits. Because created beings are not self-sufficient and cannot account for their own existence, they are fundamentally dependent on God, who serves as the unconditioned, infinite source of all being.1324