s is by grace, and not by nature.

Obj. 2: Further, the Seraphim are called "burning" or "kindling," as
Dionysius says (Coel. Hier. vii). This belongs to charity which comes
not from nature but from grace; for "it is poured forth in our hearts
by the Holy Ghost Who is given to us" (Rom. 5:5): "which is said not
only of holy men, but also of the holy angels," as Augustine says (De
Civ. Dei xii). Therefore the angelic orders are not from nature, but
from grace.

Obj. 3: Further, the ecclesiastical hierarchy is copied from the
heavenly. But the orders among men are not from nature, but by the
gift of grace; for it is not a natural gift for one to be a bishop,
and another a priest, and another a deacon. Therefore neither in the
angels are the orders from nature, but from grace only.

_On the contrary,_ The Master says (ii, D. 9) that "an angelic order
is a multitude of heavenly spirits, who are likened to each other by
some gift of grace, just as they agree also in the participation of
natural gifts." Therefore the distinction of orders among the angels
is not only by gifts of grace, but also by gifts of nature.

_I answer that,_ The order of government, which is the order of a
multitude under authority, is derived from its end. Now the end of
the angels may be considered in two ways. First, according to the
faculty of nature, so that they may know and love God by natural
knowledge and love; and according to their relation to this end the
orders of the angels are distinguished by natural gifts. Secondly,
the end of the angelic multitude can be taken from what is above
their natural powers, which consists in the vision of the Divine
Essence, and in the unchangeable fruition of His goodness; to which
end they can reach only by grace; and hence as regards this end, the
orders in the angels are adequately distinguished by the gifts of
grace, but dispositively by natural gifts, forasmuch as to the angels
are given gratuitous gifts according to the capacity of their natural
gifts; which is not the case with men, as above explained (Q. 62, A.
6). Hence among men the orders are distinguished according to the
gratuitous gifts only, and not according to natural gifts.

From the above the replies to the objections are evident.
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FIFTH ARTICLE [I, Q. 108, Art. 5]

Whether the Orders of the Angels Are Properly Named?

Objection 1: It would seem that the orders of the angels are not
properly named. For al