Objection 1. It would seem that the superior angel does not enlighten the inferior concerning all he himself knows. For Dionysius says (Coel. Hier. xii) that the superior angels have a more universal knowledge; and the inferior a more particular and individual knowledge. But more is contained under a universal knowledge than under a particular knowledge. Therefore not all that the superior angels know, is known by the inferior, through these being enlightened by the former.
Objection 2. Further, the Master of the Sentences (ii, D, 11) says that the superior angels had long known the Mystery of the Incarnation, whereas the inferior angels did not know it until it was accomplished. Thus we find that on some of the angels inquiring, as it were, in ignorance: "Who is this King of glory?" other angels, who knew, answered: "The Lord of Hosts, He is the King of glory," as Dionysius expounds (Coel. Hier. vii). But this would not apply if the superior angels enlightened the inferior concerning all they know themselves. Therefore they do not do so.
Objection 3. Further, if the superior angels enlighten the inferior about all they know, nothing that the superior angels know would be unknown to the inferior angels. Therefore the superior angels could communicate nothing more to the inferior; which appears open to objection. Therefore the superior angels do not enlighten the inferior in all things.
On the contrary, Gregory [Peter Lombard, Sent. ii, D, ix; Cf. Gregory, Hom. xxxiv, in Ev.] says: "In that heavenly country, though there are some excellent gifts, yet nothing is held individually." And Dionysius says: "Each heavenly essence communicates to the inferior the gift derived from the superior" (Coel. Hier. xv), as quoted above (Article 1).
I answer that, Every creature participates in the Divine goodness, so as to diffuse the good it possesses to others; for it is of the nature of good to communicate itself to others. Hence also corporeal agents give their likeness to others so far as they can. So the more an agent is established in the share of the Divine goodness, so much the more does it strive to transmit its perfections to others as far as possible. Hence the Blessed Peter admonishes those who by grace share in the Divine goodness; saying: "As every man hath received grace, ministering the same one to another; as good stewards of the manifold grace of God" (1 Peter 4:10). Much more therefore do the holy angels, who enjoy the plenitude of participation of the Divine goodness, impart the same to those below them.
Nevertheless this gift is not received so excellently by the inferior as by the superior angels; and therefore the superior ever remain in a higher order, and have a more perfect knowledge; as the master understands the same thing better than the pupil who learns from him.
Reply to Objection 1. The knowledge of the superior angels is said to be more universal as regards the more eminent mode of knowledge.
Reply to Objection 2. The Master's words are not to be understood as if the inferior angels were entirely ignorant of the Mystery of the Incarnation but that they did not know it as fully as the superior angels; and that they progressed in the knowledge of it afterwards when the Mystery was accomplished.
Reply to Objection 3. Till the Judgment Day some new things are always being revealed by God to the highest angels, concerning the course of the world, and especially the salvation of the elect. Hence there is always something for the superior angels to make known to the inferior.
Source: Summa Theologica (New Advent)