Enarrationes in psalmos 118, S 23, 1.
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Indeed, no creature, even though it be rational and intelligent, is enlightened by itself; it is enlightened by participation in the eternal truth and, if, sometimes, it is called ‘day’ it is not the same as ‘Day as Lord’ but the day which the Lord made. Because of this, we say to Him, ‘come to Him and you will be enlightened'.