Augustine of Hippo
Who would be audacious enough to assert that angels were created after all that was accomplished during the six days of creation? And should anyone hold such a misguided belief, their arrogance is countered by another Scripture of equal weight, where God declares, "When the stars were made, all my angels praised me with a great voice" (Job 38:7). Therefore, the angels existed prior to the creation of the stars. The stars were formed on the fourth day. Should we consider the possibility that angels were fashioned on the third day? Certainly not! For what was created on that day remains evident before us. On that day, the land was distinguished from the waters, each element took on distinct characteristics, and the earth produced all that it harbored through its roots.
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But could they have been created on the second day? This is impossible; for it was then that the firmament known as heaven was established between the lower and higher waters, upon which the stars were created on the fourth day.
Consequently, if angels are part of God's creations that occurred during those days, they are surely the light referred to as day. This day is unique and is not designated as "day one," but rather simply "day," emphasizing its singularity. It is neither the second, nor the third, nor any other day—rather, it is a repeated day, relevant for the fulfillment of both the sixfold and sevenfold count, which pertains to the knowledge of creation and divine rest. When God proclaimed, "Let there be light, and there was light," if this light appropriately signifies the creation of angels, then they indeed became participants in the eternal Light which embodies the unchangeable Wisdom of God, the Creator of all, known to us as the only-begotten Son of God. Thus, illuminated by this Light through which they were created, they became light themselves and were called day, partaking in the unalterable Light and Day, which is the Word of God, through which they too were brought into existence.
For that "true Light, which enlightens every man coming into the world" (John 1:9), also illuminates every pure angel; hence, an angel is light not of himself, but in God. Conversely, should an angel turn away from Him, he becomes impure, akin to those referred to as unclean spirits, who have ceased to be light in the Lord, enveloped in darkness due to their severance from the eternal Light. Evil is not a substance; rather, it is the absence of good that has been designated as evil.