Please briefly explain the cosmological argument for the existence of God.

In our experience of the world, everything that exists, exists because it has a cause. Nothing that exists is causeless. If so, what is it that causes everything that exists? The cosmological argument posits that there must be some 'uncaused cause', something that exists without causation, and as such grounds causation and thereby existence. In the famous phrase of St Thomas Aquinas, a major proponent of the cosmological argument, this 'uncaused cause' is what we call God. Without God, the cosmological argument claims, we would be left incapable of explaining the caused existence of the world.