An Historical Summary of Angelic Hierarchies from Part VII: The “Seven” Thrones in In Operibus Sigillo Dei Aemeth by David Richard Jones.

“Here is a brief extract that bears on their situation and gives a fourfold analysis. As in all things, St. Thomas is lucid and rigorous.

The order of the ‘Thrones’ excels the inferior orders as having an immediate knowledge of the types of the Divine works; whereas the ‘Cherubim’ have the excellence of ardor. And although these two excellent attributes include the third, yet the gift belonging to the ‘Thrones’ does not include the other two; and so the order of the ‘Thrones’ is distinguished from the orders of the ‘Cherubim’ and the ‘Seraphim.’ For it is a common rule in all things that the excellence of the inferior is contained in the superior, but not conversely. But Dionysus (Coel. Hier. vii) explains the name ‘Thrones’ by its relation to material seats, in which we may consider four things.

1. First, the site; because the seats are raised above the earth, and to the angels who are called ‘Thrones’ are raised up to the immediate knowledge of the types of things in God.
2. Secondly, because in material seats is displayed strength, forasmuch as a person sits firmly on them. But here the reverse is the case; for the angels themselves are made firm by God.
3. Thirdly, because the seat receives him who sits thereon, and he can be carried thereupon; and so the angels receive God in themselves, and in a retain way bear Him to the inferior creatures.
4. Fourthly, because in its shape, a seat is open on one side to receive the sitter; and thus are the angels promptly open to receive God and to serve Him.” [via]

St. Thomas Aquinas