For what happens to the children of man and what happens to the beasts is the same; as one dies, so dies the other. They all have the same breath, and man has no advantage over the beasts, for all is vanity.
Solomon is still showing that every thing in this world, without piety and the fear of God, is vanity. Take away religion, and there is nothing valuable among men, nothing for the sake of which a wise man would think it worth while to live in this world.
Commenting on Ecclesiastes 3:16-22
For that which befalleth the sons of men befalleth beasts,.... Aben Ezra says this verse is according to the thoughts of the children of men that are not wise; but rather the wise man says what he does according to his own thoughts, and proceeds to prove the likeness and equality of men and beasts; even one thing befalleth them; the same events belong to...
Literally, "For the sons of men (Adam) are a mere chance, as also the beast is a mere chance." These words can only be the sentiments of the skeptical oppressors. God's delay in judgment gives scope for the "manifestation" of their infidelity (Ecc 8:11; Psa 55:19; Pe2 3:3,4).