What is clear in the Biblical text
Animals have a spirit & a body, which separate at death.
Verse 20 is a synonymous parallelism. As Victor Ludlow has observed:
Parallelism is the most distinctive quality of Hebrew poetry...In
parallelism, a thought, idea, grammar pattern, or key word of the
first line is repeated or continued in the second line. There are two
basic types of parallelism, grammatical and semantic...Among the types
of semantic parallelism...Synonymous parallelism: a theme of the first
line repeats itself in the second line, but in slightly different
words (Isaiah: Prophet, Seer, And Poet p. 32)
"All go to one place" & "All are from the dust, and to dust all return" are parallel expressions conveying the same concept. By comparison to Eccl. 12:7 & Genesis 2:7 we know that this is what happens to the physical body.
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What is semi-clear in the Biblical text
Per the above, "All go to one place", then, need not say anything at all about the destinations of the spirit. This is why verse 21 asks a question--in layman's terms, the Preacher is saying:
- The bodies of men & beasts go to the same place - they molder in the earth
- I'm not sure if their spirits go to the same place
That this is a genuine question, rather than a rhetorical exercise, appears likely by comparison to Ecclesiastes' use of the same "who knows" expression in 2:19 & 6:12, where uncertainty is clearly expressed (see Pulpit commentary).
Many see evidence in the first 2 chapters of Genesis of a spiritual creation followed by a physical creation--that not just man--but other creations as well have a spirit that was created (see Genesis 1), and subsequently housed in a physical body (see Genesis 2).
A deep dive on this matter would be a post all its own; I'll just offer a brief observation from Genesis 2:4-5:
4 These are the generations of the heavens and of the earth when they
were created, in the day that the Lord God made the earth and the
heavens,
5 And every plant of the field before it was in the earth, and every
herb of the field before it grew: for the Lord God had not caused it
to rain upon the earth, and there was not a man to till the ground.
This implies that plants were created before they grew in the earth. It also calls attention to what would otherwise be a great paradox in the narrative: plants came forth in chapter 1 (see v 12), but in chapter 2 it indicates that it hasn't rained yet. One of the conclusions that can be drawn from this is that God created everything spiritually before creating it physically--and that the immortal spirit (if one believes in an immortal spirit, I do) is a feature possessed by animals as well.
(this is not to say there is no distinction between humans & beasts--it is clearly humans that are uniquely created in the image of God--see Genesis 1:27)
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What is ambiguous in the Biblical text
What do animals do in eternity & where are they? This is less clear--the Biblical texts focus so much more on the well-being & salvation of man than of beasts, there's precious little information here.
A passage sometimes employed on this matter is Revelation 4:6-9 as a description of animals in eternity before the throne of God. These animals appear to be in a positive, heavenly state, and are certainly depicted as conscious. Others will, of course, suggest this is entirely figurative.
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Up & Down
Some render the references to up & down as the comparatives above & below (see Barnes' commentary), but this interpretation is contested.
It is noteworthy that Jewish depictions of Sheol frequently had it divided into 2 sections, an upper & lower portion, leaving open the possibility that going upwards describes a spirit going to the upper portion of Sheol, and going down to the lower portion.
Further insight is offered in Proverbs:
To the wise the way of life goeth upward, that he may depart from
Sheol beneath (Proverbs 15:24)
This lends further support to the view that Sheol is an intermediate state, and that for those who are prepared, it will be followed by a more glorious future (this could also be used to argue for the resurrection of only the righteous, but Paul rules out this possibility in 1 Cor 15:22).
In this case, the spirit could go down to Sheol and then later go up to the mansions of the Father, in which case the net direction is upwards, but like hiking a large mountain, the path to the summit involves paths of descent and paths of ascent.
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Conclusion
The Biblical text offers relatively little information on what the next life looks like for animals, but if we accept the following propositions:
- Animals have a spirit (stated in Eccl. 3)
- A spirit doesn't cease to exist (I've argued for this elsewhere)
We can infer that there will be animals in eternity. Where they will be in relation to humans is less clear.