This argument, however, does not satisfy. For it holds good only in such movements as are measured by time, and take place successively; thus, if local movement follows a change, then the change and the local movement cannot be terminated in the same instant. But if the changes are instantaneous, then all at once and in the same instant there can be a term to the first and the second change; thus in the same instant in which the moon is lit up by the sun, the atmosphere is lit up by the moon. Now, it is manifest that creation is instantaneous; so also is the movement of free-will in the angels; for, as has been already stated, they have no occasion for comparison or discursive reasoning (Q. 58, A. 3). Consequently, there is nothing to hinder the term of creation and of free-will from existing in the same instant.
We must therefore reply that, on the contrary, it was impossible for the angel to sin in the first instant by an inordinate act of free-will. For although a thing can begin to act in the first instant of its existence, nevertheless, that operation which begins with the existence comes of the agent from which it drew its nature; just as upward movement in fire comes of its productive cause. Therefore, if there be anything which derives its nature from a defective cause, which can be the cause of a defective action, it can in the first instant of its existence have a defective operation; just as the leg, which is defective from birth, through a defect in the principle of generation, begins at once to limp. But the agent which brought the angels into existence, namely, God, cannot be the cause of sin. Consequently it cannot be said that the devil was wicked in the first instant of his creation.
Reply Obj. 1: As Augustine says (De Civ. Dei xi, 15), when it is stated that "the devil sins from the beginning," "he is not to be thought of as sinning from the beginning wherein he was created, but from the beginning of sin": that is to say, because he never went back from his sin.
Reply Obj. 2: That distinction of light and darkness, whereby the sins of the demons are understood by the term darkness, must be taken as according to God's foreknowledge. Hence Augustine says (De Civ. Dei xi, 15), that "He alone could discern light and darkness, Who also could foreknow, before they fell, those who would fall."
Reply Obj. 3: All that is in merit is from God; and consequently an angel could merit in the first instant of his creation. The same reason does not hold good of sin; as has been said.
Reply Obj. 4: God did not distinguish between the angels before the turning away of some of them, and the turning of others to Himself, as Augustine says (De Civ. Dei xi, 15). Therefore, as all were created in grace, all merited in their first instant. But some of them at once placed an impediment to their beatitude, thereby destroying their preceding merit; and consequently they were deprived of the beatitude which they had merited. _______________________
SIXTH ARTICLE [I, Q. 63, Art. 6]
Whether There Was Any Interval Between the Creation and the Fall of the Angel?
Objection 1: It would seem that there was some interval between the angel's creation and his fall. For, it is said (Ezech. 28:15): "Thou didst walk perfect [*Vulg.: 'Thou hast walked in the midst of the stones of fire; thou wast perfect . . .'] in thy ways from the day of thy creation until iniquity was found in thee." But since walking is continuous movement, it requires an interval. Therefore there was some interval between the devil's creation and his fall.
Obj. 2: Further, Origen says (Hom. i in Ezech.) that "the serpent of old did not from the first walk upon his breast and belly"; which refers to his sin. Therefore the devil did not sin at once after the first instant of his creation.