Honorable Rabbi,
This is the first time I've heard that in the Third Temple they won't offer animal sacrifices, so briefly—what does Rabbi Kook say they will offer?
What's the point of studying the practical laws of sacrifices?
And why aren't there laws suited specifically to the days of its construction, so that we'll be prepared…
And what will they do with the Temple vessels they've prepared? And everything connected to the sacrifices…

I didn't understand why the rabbi does not long for the restoration of the Temple service. We say:
May the Merciful One restore to us the Temple service in its place speedily in our days..

Everything starts with individuals and afterward more and more join in..

After all, once it is built, more people will come and it will be more honorable there, because we built a house for the Divine Presence.

I am not an expert in Rabbi Kook's teaching. My understanding is that he held they would offer from the plant realm (meal-offerings). Studying the laws of sacrifices, like Torah study in general, is not specifically in order to fulfill them. Otherwise, why study the passage and laws of the stubborn and rebellious son? After all, our tradition is that there never was and never will be such a case. Study is a value in itself (cleaving to God's will); see the beginning of the Book of Tanya and Nefesh HaChayim, Gate 4.
I do not long for it because I find it hard to identify with a situation in which priests walk ankle-deep in the blood of animals. That really does not speak to me. On the other hand, maybe that is only a result of my distance from it and my unfamiliarity with that situation. If it returns and I can understand what it does for us, perhaps then I will understand why it is important and beneficial.

Their blood in place of our blood, Rabbi.
The person who comes to offer understands that his blood should have been there, and that shakes him up—that's the point.
The rebellious son is about disputes, and fine, "study it and receive reward." There's no problem.

But the whole matter of study is for the sake of doing, and if there is no such possibility then what's the point of studying something that supposedly will not bring me to action? Say I am a double amputee—what's the point of my studying the laws of tefillin? Wouldn't it be better for me to study commandments that do relate to me? After all, all His will, blessed be He, is that we perform commandments, and accordingly it is understood that His purpose and will is that we study what is relevant.
What is relevant in the rebellious son? We learn from it that it is forbidden to rebel against one's parents, and that if we stray from the teaching of our mother (or father of course, “Ask your father and he will tell you”) then our fate is death—even if such a case doesn't exist and never will, that knowledge is important because it adds awe and trembling and fear.
And by the way, if the rabbi is persuaded by plant offerings, fine—at least direct your prayer toward that. But not to long at all for the building of the Third Temple—I can't digest that.

Moshe,
What lesson in honoring parents do you learn from analyzing the law that a stubborn and rebellious son applies specifically during the three months after reaching majority? And what law do you learn from the fact that he must eat specifically a tartemar of meat?
And why are you studying the laws of offering sacrifices if you are not a priest?
See Rabbi Israel Salanter's article, "Law and Judgment." There he shows that study is not for the sake of doing, but in order to know (as in Nefesh HaChayim, Gate 4, and Tanya chapters 4–5).

There is a difference between saying the prayer and longing. Longing is a mental state, and if I say that I long for all this, I would be lying. And their God hates lies, as it says: “He who speaks falsehood shall not be established.”

It seems to me this brings us back to an old discussion that already took place, between remembrance and commandments in actual practice. “In your mouth and in your heart, to do it,” and “all the people said: we will do and we will hear.” “Remember” and “observe” were said in one utterance. Most verses indicate that study is directed toward action necessarily more than toward study for the sake of knowledge. Rabbi Ishmael says: one who studies Torah in order to teach, they enable him to study and to teach.

And one who studies in order to do, they enable him to study and to teach, to observe and to do. Rabbi Tzadok says: do not make them a crown with which to glorify yourself, nor a spade with which to dig. And thus Hillel would say: one who makes use of the crown passes away. Thus you have learned: anyone who derives benefit from words of Torah removes his life from the world.

On the other hand, Rabbi, there is a rule: do not separate yourself from the community. When the whole community longs for the building of the Third Temple—you too need to long for it. It's God's house; how can one not long for that? Better not to say it at all than to say it and not long for it, because then his mouth and heart are equal.

The whole point of the stubborn and rebellious son is that he eats and guzzles and has no good future in terms of sanctifying the purpose for which he was created; for a rebellious son it would have been better had he not been created. The rebellious son needs to be an adult, because otherwise how can you rebuke him? And they were right to specify three months, because some people's minds mature more slowly than others their age.

I'm talking about someone who does study.
Ecclesiastes also concludes: “Fear God and keep His commandments, for this is the whole of man.” So why study if there is no practical point in it for someone? In my opinion, even in study there is a priority as to what to study, who is studying, and when!
There is no point in teaching a boy of commandment age the laws of niddah… and there is no point in teaching a girl the laws of tefillin or tzitzit.

From beginning to end these are astonishing words that make the rafters tremble. But I have already said my piece.