Likutei Moharan, Part II 68:2/ליקוטי מוהר"ן·תנינא ס״ח:ב׳

12. And the inverse is also true. The tzaddik must show whoever is very lofty that he is utterly distant from God; “What have you seen? What do you know?…”

2Thus, this is the tzaddik’s perfection, as in “for kol (all) that is in heaven and on the earth” (1 Chronicles 29:11), which is the concept of the tzaddik, as is known, because he unites heaven and earth. That, as mentioned above, he should be above and below, showing whoever is above, the concept of “heaven,” that it is the reverse—that he is very distant and knows nothing at all of Godly Knowledge; the concepts of “What have you seen? What do you know?” because there, above, in heaven—specifically there, they ask “Where is the place of His glory?” And inversely, he shows whoever is genuinely below, in the earth, that God is with him, because “the whole earth is filled with His glory.” Thus, this is the essence of perfection, being above and below.

3And this is the concept of the sons and disciples which one has to leave behind in the world. On the face of it, the matter is puzzling. Is not the essential thing that a person must dissociate himself completely from physicality? That being so, why is it that when a person ascends on high entirely, i.e., after passing away, he has an obligation to leave behind sons in this physical world, who will take his place in the world? On the contrary, is it not better to ascend on high entirely?

4However, in fact, genuine perfection is to be above and below, in heaven and on the earth. This is because when he is in just one world, it is not perfection. Only the two together, above and below—that is a complete world. A person is therefore required to leave behind “a remnant on earth” (Genesis 45:7), a son or a disciple, so that when he is above, after passing away, he will also be below, in this world—i.e., he leaves below a son or a disciple who stems from him.

5And the essence is the mind; that some of his mind should remain below. Therefore, he has to leave behind a son or a disciple, as our Sages, of blessed memory, expounded the verse: “who have no replacement” (Psalms 55:20)—one opines that it refers to a son, and the other opines that it refers to a disciple (Bava Batra 116a). For the disciple stems from the mind of the teacher, and likewise, the son too stems from the mind of the father. Thus, Rabbi Yochanan, because he had no sons, maintained that it refers to a disciple. In the case of the disciple, the mind is entirely removed from physicality, whereas in the case of the son the mind is encompassed in the drop of seed. Nevertheless, this, too, is needed.