I answer that, Natural knowledge and love remain in the angels. For as principles of operations are mutually related, so are the operations themselves. Now it is manifest that nature is to beatitude as first to second; because beatitude is superadded to nature. But the first must ever be preserved in the second. Consequently nature must be preserved in beatitude: and in like manner the act of nature must be preserved in the act of beatitude.
Reply Obj. 1: The advent of a perfection removes the opposite imperfection. Now the imperfection of nature is not opposed to the perfection of beatitude, but underlies it; as the imperfection of the power underlies the perfection of the form, and the power is not taken away by the form, but the privation which is opposed to the form. In the same way, the imperfection of natural knowledge is not opposed to the perfection of the knowledge in glory; for nothing hinders us from knowing a thing through various mediums, as a thing may be known at the one time through a probable medium and through a demonstrative one. In like manner, an angel can know God by His essence, and this appertains to his knowledge of glory; and at the same time he can know God by his own essence, which belongs to his natural knowledge.
Reply Obj. 2: All things which make up beatitude are sufficient of themselves. But in order for them to exist, they presuppose the natural gifts; because no beatitude is self-subsisting, except the uncreated beatitude.
Reply Obj. 3: There cannot be two operations of the one faculty at the one time, except the one be ordained to the other. But natural knowledge and love are ordained to the knowledge and love of glory. Accordingly there is nothing to hinder natural knowledge and love from existing in the angel conjointly with those of glory. _______________________
EIGHTH ARTICLE [I, Q. 62, Art. 8]
Whether a Beatified Angel Can Sin?
Objection 1: It would seem that a beatified angel can sin. For, as as said above (A. 7), beatitude does not do away with nature. But it is of the very notion of created nature, that it can fail. Therefore a beatified angel can sin.
Obj. 2: Further, the rational powers are referred to opposites, as the Philosopher observes (Metaph. iv, text. 3). But the will of the angel in beatitude does not cease to be rational. Therefore it is inclined towards good and evil.
Obj. 3: Further, it belongs to the liberty of free-will for man to be able to choose good or evil. But the freedom of will is not lessened in the beatified angels. Therefore they can sin.
On the contrary, Augustine says (Gen. ad lit. xi) that "there is in the holy angels that nature which cannot sin." Therefore the holy angels cannot sin.