It is very dangerous to teach a Torah lesson. It takes great effort and abundant skill to be able to weigh one’s words so that each listener hears only what he has need of and no more.

Thus, although everyone hears the entire Torah lesson he delivers, each person hears solely what he needs to. This is as is brought concerning the verse “And Yitro heard” (Exodus 18:1)—but surely the whole world heard? However, Yitro heard… (Zohar II, 68a). Yitro’s hearing alone is considered hearing, in that it entered his ears. The hearing of the rest of the world is not considered hearing at all.

Now, whoever cannot deliver a Torah lesson in this fashion is forbidden to teach Torah. This is because when each person comes to the tzaddik to hear Torah, his evil comes along with him—i.e., the kelipot (evil forces) created through sin, God forbid. They are the ones who crowd people and create disarray and a great crush at the time the Torah lesson is being given, because each person’s evil seeks to confuse. This is as our Sages, of blessed memory, taught: That crowding at public lectures is due to them (Berakhot 6a)—i.e., from each one’s evil, namely, the kelipot.

And these kelipot, too, seek to sustain themselves from the Torah lesson. But their sustainment is only from the excesses—i.e., that which someone hears which is too much or too high for his mind and comprehension. This is the concept of excesses, and they sustain themselves from there. It is also the concept of the Torah’s secrets being given over to the external forces. For their sustainment is from the Torah’s esoteric teachings—i.e., from that which is beyond a person’s mind, each according to the extent of his comprehension.

Therefore, the sage who teaches Torah must possess the aforementioned skill, so that not one of the listeners hears what is unsuitable for his mind and comprehension—which is not relevant to him—so as not to enable [the kelipot] to sustain themselves, God forbid.

And know! there is a subtle kelipah which is close to holiness. This subtle kelipah is capable of sustaining itself from even the body of the Torah lesson itself, even if it contains no excesses. The remedy for this is talking of Jewish salvation, as then that subtle kelipah flees.

This is what our Sages, of blessed memory, taught: Yitro came and left before the Giving of the Torah (Zevachim 116a). Yitro is the concept of the subtle kelipah that flees when it hears of Jewish salvation.

And when the true tzaddik teaches Torah, he has greater awe than the awe associated with Rosh HaShanah and Yom Kippur.