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. But when there is nothing to retard or thwart it, nature is moved with its whole energy.
As was observed above an angel has nothing in him to retard his action, and with his whole might he is moved to whatsoever he is moved, be it good or bad.
Consequently man’s will adheres to a thing movably, and with the power of forsaking it and of clinging to the opposite; whereas the angel’s will adheres fixedly and immovably.
Therefore, if his will be considered before its adhesion, it can freely adhere either to this or to its opposite, but after he has once adhered, he clings immovably. So it is customary to say …the angel’s free-will is flexible either opposite before the choice, but not after. Therefore the good angels who adhered to justice, were confirmed therein; whereas the wicked ones, sinning, are obstinate in sin.