"In modern philosophical terminology, Aquinas is arguing along the following lines:
Things exist in the world around us that exhibit finite degrees of great-making properties (e.g. being, goodness, truth, beauty)
The existence of something exhibiting a great-making property to a finite degree implies the existence of something that possesses the property in question to a maximal degree
Therefore, all great making properties possessed in finite degree by beings in the world around us, including being, are possessed to a maximal degree by something
An effect cannot exceed the greatness of its cause
- Therefore, there exists a maximally ontologically secure being that possess every great-making property possessed by its effects to a maximal degree; and this we call God.