It is…in wisdom literature that quotations play the most fundamental role. Here, there is no supernatural revelation, merely patient observation used as the basis of reasonable conclusions. Each generation of Sages finds in the extant proverbial literature of the past a body of truth, created by their predecessors, whose observations on life have approved themselves to their colleagues.
Robert Gordis, Koheleth – The Man and His World: A Study of Ecclesiastes, 3rd ed. (Shocken Books: New York, 1968), 95-96.