All the rivers flow into the sea, yet the sea is never full; to the place from which the streams come, there again they flow.
To prove the vanity of all things under the sun, and their insufficiency to make us happy, Solomon here shows, 1. That the time of our enjoyment of these things is very short, and only while we accomplish as a hireling his day. We continue in the world but for one generation, which is continually passing away to make room for another, and we are passing with it.
Commenting on Ecclesiastes 1:4-8
All the rivers run into the sea; yet the sea is not full,.... Which flow from fountains or an formed by hasty rains; these make their way to the sea, yet the sea is not filled therewith, and made to abound and overflow the earth, as it might be expected it would.
By subterraneous cavities, and by evaporation forming rain clouds, the fountains and rivers are supplied from the sea, into which they then flow back. The connection is: Individual men are continually changing, while the succession of the race continues; just as the sun, wind, and rivers are ever shifting about, while the cycle in which they move is invariable; they return to the point whence they set out.