Thomas Aquinas

“ If the end is within the power of the rational creature, then its action is said to procure the end; as man acquires knowledge by reflection: but if the end be beyond its power, and is looked for from another, then the action will be meritorious of such end. But what is already in the ultimate term is not said to be moved, but to have been moved. Consequently, to merit belongs to the imperfect charity of this life; whereas perfect charity does not merit but rather enjoys the reward. Even as in acquired habits, the operation preceding the habit is productive of the habit ”

“ For the intellect cannot but assent to naturally known principles; in the same way, the will cannot help clinging to good, formally as good; because the will is naturally ordained to good as to its proper object. Consequently the will of the angels is referred to opposites, as to doing many things, or not doing them. But they have no tendency to opposites with regard to God Himself, Whom they see to be the very nature of goodness; but in all things their aim is towards God, which ever alternative they choose, that is not sinful. ”

“ Further, an angel could act at once, and in an instant, from the very outset of his creation, for even natural bodies begin to be moved in the very instant of their creation; and if the movement of a body could be instantaneous, like operations of mind and will, it would have movement in the first instant of its generation. Consequently, if the angel merited beatitude by one act of his will, he merited it in the first instant of his creation; and so, if their beatitude was not retarded, then the angels were in beatitude in the first instant. ”

“ But as the angel is of his nature inclined to natural perfection, so is he by merit inclined to glory. Hence instantly after merit the angel secured beatitude. Now the merit of beatitude in angel and man alike can be from merely one act; because man merits beatitude by every act informed by charity. ”

“ But when there is nothing to retard or thwart it, nature is moved with its whole energy. So it is reasonable to suppose that the angels who had a higher nature, were turned to God more mightily and efficaciously. The same thing happens in men, since greater grace and glory are bestowed according to the greater earnestness of their turning to God. ”

“ To be turned to his ultimate beatitude is difficult for man, both because it is beyond his nature, and because he has a hindrance from the corruption of the body and infection of sin. But it is difficult for an angel, only because it is supernatural. ”

“ Hence some writers say that they can merit as to their accidental reward. But it is better to say that the Blessed can in no wise merit without being at the same time a wayfarer and a comprehensor; like Christ, Who alone was such. For the Blessed acquire such joy from the virtue of their beatitude, rather than merit it. ”

“ Further, the angelic nature is nobler than the corporeal creature. But the corporeal creature straightway from its creation was made perfect and complete; nor did its lack of form take precedence in time, but only in nature, as Augustine says (Gen. ad lit. i, 15) . Therefore neither did God create the angelic nature imperfect and incomplete. But its formation and perfection are derived from its beatitude, whereby it enjoys God. Therefore it was created in beatitude. ”

“ It would seem that the angel did not possess beatitude instantly after one act of merit. For it is more difficult for a man to do well than for an angel. But man is not rewarded at once after one act of merit. ”

“ I answer that, The angel was beatified instantly after the first act of charity, whereby he merited beatitude. The reason whereof is because grace perfects nature according to the manner of the nature; as every perfection is received in the subject capable of perfection, according to its mode. Now it is proper to the angelic nature to receive its natural perfection not by passing from one stage to another ”

“ But since infinite efficacy is required for comprehending God, while the creature's efficacy in beholding is only finite; and since every finite being is in infinite degrees removed from the infinite; it comes to pass that the rational creature understands God more or less clearly according to infinite degrees. And as beatitude consists in vision, so the degree of vision lies in a determinate mode of the vision. ”

“ Consequently no rational creature can have the movement of the will directed towards such beatitude, except it be moved thereto by a supernatural agent. This is what we call the help of grace. Therefore it must be said that an angel could not of his own will be turned to such beatitude, except by the help of grace.
Reply to Objection 1: The angel loves God naturally, so far as God is the author of his natural being. But here we are speaking of turning to God, so far as God bestows beatitude by the vision of His essence.
Reply to Objection 2: A thing is "difficult" which is beyond a power ”

“ Diversity of natural gifts is in one way in the angels, who are themselves different specifically; and in quite another way in men, who differ only numerically. For specific difference is on account of the end; while numerical difference is because of the matter. Furthermore, there is something in man which can thwart or impede the movement of his intellective nature ”

“ In another way a thing may be beyond the power, not according to the natural order of such power, but owing to some intervening hindrance; as to mount upwards is not contrary to the natural order of the motive power of the soul; because the soul, considered in itself, can be moved in any direction ”

“ Secondly, the same is evident on the part of the angel. The angel is not a compound of different natures, so that the inclination of the one thwarts or retards the tendency of the other; as happens in man, in whom the movement of his intellective part is either retarded or thwarted by the inclination of his sensitive part. ”

“ For it is impossible that as the rational creature is led on to the vision of the Supreme Essence, it should be led on in the same way to the supreme mode of vision, which is comprehension, for this belongs to God only ”

“ In this way the angelic ministerings are useful for the beatified angels, inasmuch as they are a part of their beatitude; for to pour out acquired perfection upon others is of the nature of what is perfect, considered as perfect.
Reply to Objection 3: Although a beatified angel is not absolutely in the highest degree of beatitude, yet, in his own regard he is in the highest degree, according to Divine predestination. Nevertheless the joy of the angels can be increased with regard to the salvation of such as are saved by their ministrations, according to Lk. ”