Commentaire sur Haguiga 2:1

אין דורשין בעריות – to three people as one [i.e., together], we do not expound the secrets of the illicit sexual relationships, such his daughter from his outraged woman, which is not written in Scripture explicitly lest at the time when the Rabbi speaks with one, the other two will discuss it between them, and they will not give their hearts over to listen from the mouth of the Rabbi when he expounds upon this prohibition. But they will come to be lenient in illicit sexual relationships on account of the fact the soul of a person yearns for them and covets them more than the rest of the prohibitions of the Torah.

They may not expound upon the subject of forbidden relations in the presence of three.
Nor the work of creation in the presence of two.
Nor [the work of] the chariot in the presence of one, unless he is a sage and understands of his own knowledge.
Whoever speculates upon four things, it would have been better had he not come into the world: (1) what is above, (2) what is beneath, (3) what came before, and ( what came after.
And whoever takes no thought for the honor of his creator, it would have been better had he not come into the world.
This mishnah is brought here because like yesterday’s mishnah it may refer to certain reasons why sages abandoned the world of Torah. There are some subjects which are, according to our mishnah, dangerous to speculate upon or to discuss in front of the masses. Pondering upon the unknowable may have contributed towards apostasy.
Section one: The danger of expounding upon the verses about forbidden relations in the Torah is either that people will be confused and make irreparable mistakes (i.e. create mamzerim) or that they will be titillated by the attention paid to these verses and they will not be able to control their urges and they will come to sin. Therefore, these verses are not expounded before even a group as small as three.
Section two: How the world was created and whether it was created from already existing material was a much debated and sensitive issue in the ancient world. That there might have been material which pre-existed God would have been seen by the rabbis to be heretical. Due to the speculative nature of this subject, it was forbidden to talk about it in front of even two people.
Section three: The study of the chariot, Ezekiel’s heavenly vision (Ezekiel 1) is the mystical study of God, God’s physical attributes and God’s unknowable mysteries. The sages seem to have believed that God had a physical existence, perhaps even a body in a certain sense, but that God’s body was hidden from human beings. It was forbidden for one sage to teach this subject to another sage unless the learning sage could understand things without really being explained to them. What this seems to mean is that one sage could begin to discuss this topic with another sage but he shouldn’t reveal to him the secrets of God unless he sees that the sage understands and can proceed on his own. However, we interpret this, what is clear is that the sages were extremely hesitant to engage publicly in mysticism.
Section four: There were some things that humans couldn’t know and therefore should not try to know. They are: 1) what is above the sky; 2) what is below the earth; 3) what came before the earth was created; 4) what will come after it is destroyed. Again, these four subjects are (or at least were) completely speculative. A person should spend their time in this world studying subjects that are knowable, such as the interpretation of Torah and halakhah. Metaphysical speculation was ruled out by this mishnah. The final line of the mishnah seems to be a continuation of the previous line. Those who try to uncover God’s secrets and reveal them to the public are not acting with respect to God’s honor. It is almost as if they are undressing God in public. Had God wanted these secrets to be revealed they would have been revealed.
I should note that there do seem to have been rabbis in this period who did engage in such speculative study and even composed works dedicated to the topic. There are two ways to justify this mishnah with those other works. First of all, there were different groups of rabbis, some of which focused on halakhah/midrash and others who focused on mysticism. The second possibility, which I believe to be more likely, is that the rabbis thought that mysticism was not an appropriate focus for most people’s study. Mysticism, which they considered dangerous, should be reserved for the elite and not spread to the masses.

ולא במעשה בבראשית – in the event of the six days of creation even for [between] two people, and all the more so, for three or more, as it states in the Biblical verse (Deuteronomy 4:32): “You have but to inquire about bygone ages that came before you, [ever since God created man on earth from one end of heaven to the other: has anything as grand as this ever happened, or has its like ever been known?]. An individual can ask, but not two individuals.

ולא במעשה מרכבה – that Ezekiel saw and that Isaiah saw. And Maimonides explained, that the event of Creation, the natural wisdom, and the episode of the Chariot, which is the reality of God and his attributes, and the angels and the soul and the intellect/intuition, and what will be after death. But it does not appear to me that all of this will be called the episode of the Chariot, for if so, the wisdom of the chariot he (i.e., the Tanna of our Mishnah) should have taught, but the event of the Chariot is that via the mention of the names of holiness, we make use of the crown, and we look out how the angelic watches while they at their prayer meetings, and how the hall containing the golden altar is inside from the hall containing the golden altar, such as those who foresee the Holy Spirit.

ביחיד אלא א"כ היה חכם ומבין מדעתו – even for another person, we don’t explain the event of the Chariot, other than if the Rabbi knows him to be wise for if he would transmit to him “chapter-headings,” he would understand the rest from his own mind.

כל המסתכל בד' דברים – those that are explained further on.

ראוי לו – it is pleasant and it would be good for him if he had not come into the world.

מה למעלה – from the heads of the [divine] creatures.

מה למטה – from under the ground.

מה לפנים – outside the compartment of the firmament in the east.

ומה לאחור – to the west. Another explanation: what is before – prior to the creation of the world. And was is behind, at the end of the world and in the end of days.

כל שלא חס על כבוד קונו – that he violates a transgression in secret and states that God’s presence is not found here and who will see me and who will inform me.