I’m kind of struggling with this passage, but the main idea seems to be found in verse 18: “I said in my heart, ‘Concerning the condition of the sons of men, God tests them, that they may see that they themselves are like animals.'”
What? God tests us to show us that we are like animals?
Just like the animals, men die. Just like the animals, men return to dust. “Man has no advantage over animals, for all is vanity.” So our existence on earth is no more significant than that of any animal on the earth? That’s depressing. But I don’t think that’s exactly what this is saying.
Verse 21 says, “Who knows the spirit of the sons of men, which goes upward, and the spirit of the animal, which goes down to the earth?” So obviously man has to have more significance if his spirit goes upward (to heaven) when he dies and the spirit of an animal remains here on the earth after death.
Another version (ESV) says it this way, “Who knows whether the spirit of man goes upward and the spirit of the beast goes down into the earth?”
Now it all makes sense! God judges men, and those who waste their lives find out that their lives mattered nothing more than those of animals. They go through life wasting their energies and resources by accomplishing nothing of true value. They die and return to dust just like the animals.
But man cannot see the heart like God can, so only God will justly judge everyone’s works. Only God knows where the spirit of each person ends up, whether it goes to heaven or stays in the earth like an animals.
Just another reminder to make my life worth something for God.
When God judges man, His judgment is just.
Man truly sees the things he has done.
And just as animals return but to dust,
So do the men who worked in vain ‘neath the sun.