Then (and) I saw that wisdom excelleth folly, as far as light excelleth darkness; or, there is profit, advantage to wisdom over folly, as the advantage of light over darkness. This result, at any rate, was obtained—he learned that wisdom had a certain value, that it was as much superior to folly, in its effects on men, as light is more beneficial than darkness.
It is a natural metaphor to represent spiritual and intellectual development as light, and mental and moral depravity as darkness (comp. Ephesians 5:8; 1 Thessalonians 5:5).