If King David, who learned nothing from Achitofel except for two things alone, nevertheless referred to him as his "master," "guide," and "intimate,” it certainly goes without saying that one who learns from his fellow a single chapter, a law, a verse, a saying, or even a single letter of Torah, is obligated to revere him.

Ethics of the Fathers, 6:3

            

The Talmud compares the teachings of Torah to seedlings: Just as a seedling is fruitful and multiplies, so, too, the words of Torah are fruitful and multiply. Once implanted in the mind of its student, a single concept of Torah geminates, develops and proliferates, yielding insight upon insight as its possessor goes through life. In the words of the Zohar, "there is not a word or a tiny letter in the Torah upon which do not hang many secrets of Divine wisdom."

The phrase, "fruitful and multiply," is a reference to G‑d's blessing to the first man and woman, "Be fruitful and multiply, fill the earth, and conquer it." Indeed, the conception and development of knowledge in mind of the student parallels the conception and development of a life in the womb of the mother.

Our sages tell us, "There are three partners to the creation of man: G‑d, his father, and his mother." The capacity to procreate is, in essence, a distinctly Divine nature. All our other faculties—sight, hearing, etc.--are finite in scope; not so when it comes to our regenerative powers. Children multiply into grandchildren and great-grandchildren ad infinitum. There is no inherent limit as to how many generations can issue from a single union between man and woman. Thus, the express input of the "Third Partner": only the Creator Himself can imbue two finite creatures with infinite potential.

The same is true regarding the "regenerative power" contained in a teaching: when G‑d is a partner to their endeavor, the teacher-student relationship yields an infinite progeny. But unlike physical procreation, where the Almighty unequivocally bestows the gift of infinity to every conception, here the "Third Partner" participates by invitation only. If the teaching and pursuit of wisdom are towards positive and G‑dly ends, then the seed implanted by the teacher is "fruitful and multiplied" in the mind of his student. But if they are nothing more than an exercise in self-enhancement, then the knowledge gained does not transcend the intrinsic finiteness of its imparter and its conceiver.

Sterile Wisdom

Therein lies the answer to the oft-asked question: Can one gain positive knowledge from a bad person? The answer is yes, but with a significant difference. Assuming that one is able to separate the good from the bad, one can learn from a wicked teacher; what one will receive, however, is sterile wisdom, ideas that lack the regenerative quality to "be fruitful and multiply" and extend to infinite applications.

This explains the otherwise difficult wording in the Mishnah quoted at the opening of this essay. Why does it "certainly go without saying that one who learns from his fellow ... even a single letter of Torah, is obligated to revere him" from David's reverence of Achitofel? By the Mishnah's own attestation, David actually learned "two things" from Achitofel. Also, why the seemingly redundant terminology, "he learned nothing from Achitofel except for two things alone"?

But this is "Achitofel the Wicked," the profferer of evil consul to Absalom in his rebellion against David. So, if on two occasions, King David learned something from Achitofel, these remained "nothing except for two things alone"--lessons consisting only of their actual message and import.

Nevertheless, David revered him as his teacher. How much more so, derives the Mishnah, must a person revere one from whom he learns even a single point of wisdom—a single point in which G‑d has a part, a single point that will continue to grow and diversify within him to address the myriad challenges to confront him as he grows through life.