The Book of Kohelet is “best described as a cahier or notebook, into which the author jotted down his reflections…”
…it is clear that the Book of Koheleth is not a debate, a dialogue, or a philosophical treatise. It is best described as a cahier or notebook, into which the author jotted down his reflections during the enforced leisure of old age. They differ in mood, in style, and in length. … Its unity is not one of logical progression, but of mood and world-view.
Robert Gordis, Koheleth – The Man and His World: A Study of Ecclesiastes, 3rd ed. (Shocken Books: New York, 1968), 110.