I like the way Augustine puts this:
For I did not know that the soul needs to be enlightened by light from outside itself, so that it can participate in truth, because it is not itself the nature of truth. (IV.25)
Likely this choice of wording comes both from his affiliation with the Manichees as much as the biblical references the paragraph notes, the light versus the dark representing most often good versus evil. Augustine’s take on good and evil is more similar to a sliding scale and knowledge and acceptance of God is the weighing balance.