Dear friend, my most beloved saint is called the Angelic Doctor of the Church. Aquinas was not only angelic in his mystical knowledge of God, but he wrote extensively on angels. Like his dear friend Bonaventure, St. Thomas saw the works of the Areopagite. This fascinating early Christian writer gave us the notion of the nine angelic hierarchies. Our beloved brother Aquinas took this as a sign that he ought to write extensively on the nature of angels, and their ordering in the Universe.
Here is the section of his Summa Theologiae (Part 1) dealing with Angels, if you’re interested in a long, winding set of catechism-like questions and answers:
dhspriory.org/thomas/summa/FP.html#TOC03
Bonaventure, being a wily Franciscan

, used the seraphic qualities to describe the mind’s journey to God in several stages, the Seraphic Level being the highest level of holiness in the eyes of the Lord. Incidentally, Bonaventure used the fact that the seraphim are at the top of the Hierarchy to describe St. Francis of Assisi, who Bonaventure called ‘seraphic’; as in: burning with the highest love for God.
Angels are our brother-creatures, but grasp things perfectly upon their immediate creation. We are quasi-angelic in our higher intellect; or, angels are quasi-human in their lower intellect! The angels love us, as God commands, and they help us. St. Thomas estimates the number of angels to be so great that counting them would be as pointless as counting the stars in the sky:
(Summa 1, Q. 50, A. 3)
“…it must be said that the angels, even inasmuch as they are immaterial substances, exist in exceeding great number, far beyond all material multitude. This is what Dionysius says (Coel. Hier. xiv): “There are many blessed armies of the heavenly intelligences, surpassing the weak and limited reckoning of our material numbers.” The reason whereof is this: because, since it is the perfection of the universe that God chiefly intends in the creation of things, the more perfect some things are, in so much greater an excess are they created by God. Now, as in bodies such excess is observed in regard to their magnitude, so in things incorporeal is it observed in regard to their multitude. We see, in fact, that incorruptible bodies, exceed corruptible bodies almost incomparably in magnitude; for the entire sphere of things active and passive is something very small in comparison with the heavenly bodies. Hence it is reasonable to conclude that the immaterial substances as it were incomparably exceed material substances as to multitude.”
The better a thing is, the more God makes of it.

Think of that the next time you see an ant-hill…

and imagine that angels are much better, so there are even greater numbers! There are only fewer humans than ants because of our unfortunate tendency to kill each other, I assume.
