To answer to this question we have to well understand a couple of points:
1) Has the particle מי (mi) – a component of the expression we usually translate ‘Who knows?’ (contained in Qoe 3:21) - always implemented in it an uncertainty sense?
2) What is the meaning of רוח (mainly translated ‘spirit’, also in Qoe 3:21)? Maybe a number of Bible readers will be surprised to know what the Word of God tells about this topic.
Let’s start with the point 1 (“Has the particle מי (mi) – a component of the expression we usually translate ‘Who knows?’ - always implemented in it an uncertainty sense?”)
First of all, we must say that מי (mi) works - very often – as an interrogative pronoun, but sometimes the interrogative sense is missing (see table below). Other times this particle denotes a real question, expecting an answer; other times it introducing a mere rhetorical question (without a desired real answer).
So, sometimes מי (mi) may highlight an uncertainty sense. Yet, other times there’s no uncertainty sense (see table below).
The point (told by Hold to the Rod) that presents, that
“[…] likely by comparison to Ecclesiastes’ use of the same ‘who knows’
expression [יודע מי, mi iudo] in Qoe [Ecclesiastes] 2:19 & 6:12, where
uncertainty is clearly express […]”
has thin value for our argument, because the presence/absence of a sense of uncertainty does not depend on a binomial nomenclature, as יודע מי (mi iudo, ‘Who knows?’), or as יתן מי (mi itn, ‘Who give?’), or others; instead it depends solely by the particle מי, taking into an account the context, obviously.
Really, the inspired writer of Qoeleth (Ecclesiastes) made a rhetorical question in 3:21. Is there an uncertainty sense in it? If we consider the whole context of Qoe the answer is No. Let us consider the facts. If we pose the assumption that the question in Qoe 3:21 included an uncertainty sense, the patent ‘certainty’ sense of the declaration of Qoe 12:7 (about the destiny of man’s spirit) makes us change our mind. The inspired writer was not unsure about the destiny of man’s spirit. In fact, Qoeleth said, that it, namely, “the spirit”, “goes back to God who gave it” (Bible in Basic English). So, no uncertainty at all (in Qoeleth’s talk).
Point 2 (What is the meaning of רוח?)
A lot of years ago I examined above 160 occurrences of the term רוח in the Hebrew Bible. From this exam I (and now you also) concluded that רוח has, basically, 5 meanings (namely, five manners to translate this Hebrew term in languages as English, or Italian too). Now I listed them, along with some samples of occurrences of each of this ‘meanings’ (Kri = Judges):
1) A motivating attitude of a person (Gen 26:35; 45:27; Num 5:14, 30; 14:24; Jos 2:11; Kri 9:23; et caetera)
2) A physical wind, air in motion, or, some directions indicate by windrose (Gen 8:1; Exo 10:13; et caetera)
3) A spiritual (namely, non-material) being (2 Sam 22:11; Psa 18:10 ; 104:4; Isa 31:3; et caetera)
4) A dynamic and biologic (material) energy belonging to an individual (Gen 7:15, 22; Exo 6:9; Kri 15:19; et caetera)
5) The specific רוח belonging to God (Gen 41:38; Exo 31:3; Num 24:2; Kri 11:29; et caetera)
We have well to remember that all these ‘meanings’ – in the Hebrew language of the Bible – were focused in a single term, רוח. We, other-than-Hebrew speakers, are obliged to parcel the unique term רוח in 5 different ‘meanings’ since we have no single term (in our languages) that is able to contain all these 5 ‘meanings’. This is a very important concept we have to not forget. What we today consider five distinct concepts, the ‘biblical’ Hebrew speakers of old expressed in an unique term, רוח. From this we have to infer – by logic - that those (that we consider 5 different) ‘meanings’ are all linked by a semantic fil rouge, namely, a basic idea that connects them all.
What is this idea?
Something that is…
… invisible to human eyes
… in a potential dynamic stance
… performing/motivating some actions.
So, we cannot confound רוח with ‘soul’ (נפש). They are two different Hebrew terms, with two different meanings (but this is not the time to deepen our understanding about this other term, נפש).
Return, now, to Qoe 3:21. What is the רוח that return to God? Obviously, the fourth meaning listed above, namely, the dynamic and biologic (material) energy belonging to an (human or animal) individual.
Is it different from the body? Sure, with the same difference that exists between (for an example, not perfectly fitting one, pardon me) a brand-new Formula One’s Car with a dead battery, compared to a twin brand-new Formula One’s Car with a full-charged battery! The perfect Formula One’s Car is the ‘body’, the full-charged battery, or, better, the energy contained in the battery, is the רוח (‘spirit’).
So, according Qoeleth (12:7), the returning to God of the human רוח means simply that, in that instance, devolves to God to do a ‘recharge’ of energy (in this event, a human resurrection implies also a ‘new body’…), or not.
What about animals? First of all, in the preceding verses of Qoe 12:7, namely, Qoe 12:1-6 we see a description of human physiological decay, only. No mention there of animal physiological decay. We cannot suppose either that the animal world would be implicit in this description. See, please, how some superior prerogatives (compared to those animal’s) are involved in the Qoeleth’s speech. The writer (v. 1) calls the faithful servants of God to remember Him at the height of one’s physical/mental health, particularly, “before the evil days come, and the years draw nigh, when thou shalt say: ‘I have no pleasure in them’.” (JPS).
‘Remembering’ (or, ‘taking an account of’) God, as well as, self-reflections about our spiritual conditions are all actions out of the range of animals. So, the conclusion of Qoe 12:7 – about spirit’s destiny - does not apply to them.
Another point. Cannibalism is still – very rightly - a repulsive action to perform, right? Moreover – also to highlight the atrocity of this conduct it is – biblically speaking – listed among the divine execrations that would descend on rebellious human behaviours (Lev 26:27-29; Deu 28:53-57; 2 Kin 6:28-30).
Now, if animals were equivalent to human, as regards their spirits (that is, about if the spirit of an animal ‘returns’ to God or not), then also animals are comparable to humans about its destiny. They would possess the same dignity level of humankind (some people think that they will have also the eternal life in heaven…). But if this would be the spiritual condition of animals, virtually, a levelling of them respect to humans, why God said: “Every moving thing that liveth shall be for food for you; as the green herb have I given you all” (Gen 9:3)? Had God Himself introduce – in a very archaic epoch – cannibalism as a practice/custom for humans, also for his servants?
Thus, is evident that even though animals play a part in the humans environment, enhancing our life delight, and relieve us from a lot of dispiriting jobs too, animals have no hope that their ‘spirits’ return to God, with the possibility to live forever (see please, too, the inspired and outspoken statements of Paul an Peter, in 1 Cor 9:9; 2 Pet 2:12).
I hope these notes will be useful for your ‘investigation’.