Aquinas must have been an interesting fellow to know. I tried years ago to watch “Thomism” on EWTN. WHOOSH! Straight over my head!
Check out aquinasonline.com
It gives as concise an overview of Thomas’ philosophy as possible.
Peter Kreeft has an insightful way of classifying philosophical systems.
The first kind seem clear at first, but become obscure upon deeper study. Examples would be the British philosophers (utilitarianism).
The second group begins obscurely and ends obscurely. This would be French and German philosophy.
The final group would be those that begin obscurely but becomes clear upon deeper study. Examples would be Aristotle and Aquinas.
That’s been my experience with Aquinas. Once you understand the fundamentals of Aristotle’s philosophy, like the Four Causes, Potency/Act and Substance/Accident, things become very clear.