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. T