According to Aquinas, God is a first cause, both as the cause of the universe's coming into existence and as the cause of its being preserved in existence from one instant to the next.

First Cause

A philosophical and theological concept referring to the initial cause of the universe, often discussed in arguments for the existence of God or a prime mover.

Aquinas

A medieval philosopher and theologian, Thomas Aquinas is known for integrating Aristotelian philosophy with Christian doctrine, emphasizing ethics, natural law, and metaphysics.