Objection 1. It would seem that an inferior angel can enlighten a superior angel. For the ecclesiastical hierarchy is derived from, and represents the heavenly hierarchy; and hence the heavenly Jerusalem is called "our mother" (Galatians 4:26). But in the Church even superiors are enlightened and taught by their inferiors, as the Apostle says (1 Corinthians 14:31): "You may all prophesy one by one, that all may learn and all may be exhorted." Therefore, likewise in the heavenly hierarchy, the superiors can be enlightened by inferiors.
Objection 2. Further, as the order of corporeal substances depends on the will of God, so also does the order of spiritual substances. But, as was said above (Question 105, Article 6), God sometimes acts outside the order of corporeal substances. Therefore He also sometimes acts outside the order of spiritual substances, by enlightening inferior otherwise than through their superiors. Therefore in that way the inferiors enlightened by God can enlighten superiors.
Objection 3. Further, one angel enlightens the other to whom he turns, as was above explained (1). But since this turning to another is voluntary, the highest angel can turn to the lowest passing over the others. Therefore he can enlighten him immediately; and thus the latter can enlighten his superiors.
On the contrary, Dionysius says that "this is the Divine unalterable law, that inferior things are led to God by the superior" (Coel. Hier. iv; Eccl. Hier. v).
I answer that, The inferior angels never enlighten the superior, but are always enlightened by them. The reason is, because, as above explained (105, 6), one order is under another, as cause is under cause; and hence as cause is ordered to cause, so is order to order. Therefore there is no incongruity if sometimes anything is done outside the order of the inferior cause, to be ordered to the superior cause, as in human affairs the command of the president is passed over from obedience to the prince. So it happens that God works miraculously outside the order of corporeal nature, that men may be ordered to the knowledge of Him. But the passing over of the order that belongs to spiritual substances in no way belongs to the ordering of men to God; since the angelic operations are not made known to us; as are the operations of sensible bodies. Thus the order which belongs to spiritual substances is never passed over by God; so that the inferiors are always moved by the superior, and not conversely.
Reply to Objection 1. The ecclesiastical hierarchy imitates the heavenly in some degree, but by a perfect likeness. For in the heavenly hierarchy the perfection of the order is in proportion to its nearness to God; so that those who are the nearer to God are the more sublime in grade, and more clear in knowledge; and on that account the superiors are never enlightened by the inferiors, whereas in the ecclesiastical hierarchy, sometimes those who are the nearer to God in sanctity, are in the lowest grade, and are not conspicuous for science; and some also are eminent in one kind of science, and fail in another; and on that account superiors may be taught by inferiors.
Reply to Objection 2. As above explained, there is no similarity between what God does outside the order of corporeal nature, and that of spiritual nature. Hence the argument does not hold.
Reply to Objection 3. An angel turns voluntarily to enlighten another angel, but the angel's will is ever regulated by the Divine law which made the order in the angels.
Source: Summa Theologica (New Advent)