Before us is Mishnah 3 in the sixth chapter of Maseches Avos, which deals with the honor due to someone who taught his fellow Torah. The beraisa states: "HaLomeid meichaveiro perek echad o halachah achas o pasuk echad o dibur echad o afilu os achas - tzarich linhog bo kavod" - one who learns from his fellow a single chapter, or a single halachah, or a single verse, or a single statement, or even a single letter, must treat him with honor.
"Afilu os achas" - even a single letter: what does this mean?
Some explain that this refers to a letter that carries a halachic implication, such as the vav ha'chibur that connects the word "ve'eileh" to the preceding portion, and similar cases.
In the work Kallah Rabbati, a composition from the era of the Geonim counted among the minor tractates, whose fifth chapter deals with the sixth chapter of Avos, it is explained that even knowing the correct spelling of a word is included. For example, the discussion in Maseches Shabbos as to whether a certain word is written with a yud or an alef, regarding glowing coals. Even such a piece of knowledge, which has halachic ramifications, is enough to obligate a person to treat his fellow with honor.
An absolute obligation or a measure of piety?
It is worth noting the precise wording of the Mishnah: it does not say "chayav" (he is obligated), but rather "tzarich linhog bo kavod" - he needs to treat him with honor. From here some learn that this is only a measure of piety, and not the letter of the law as a binding technical requirement.
The precedent: David HaMelech and Achitophel:
The source for this law is derived from David HaMelech, who was the greatest of his generation, king of Israel and a link in the chain of Torah transmission, a tzaddik without equal. Achitophel served as his advisor, and Scripture testifies to the power of his wisdom, that consulting him was like literally inquiring of the word of God. And nevertheless, Achitophel was known as a corrupt scoundrel: he turned against David, sided with his son Avshalom in the rebellion, advised Avshalom to attack and kill David, and even offered to kill David with his own hands.
The Gemara in Sanhedrin counts Achitophel among those who have no share in the World to Come. Despite this, David HaMelech showed him tremendous honor for just two things that he learned from him.
The two things David learned from Achitophel:
The Gemara in Berachos (daf 63) teaches that Achitophel advised him not to learn alone, since a chavrusa keeps the learner on the straight path and catches his mistakes.
David learned from him how to enter the house of God, the beis midrash or the Mishkan, in the proper manner. Some explained that one should not walk in with an upright posture, in an arrogant and haughty way, but rather with reverence and humility; and some explained that one should not enter alone.
The basis for both of these lessons is in the verses of Tehillim chapter 55, in which David HaMelech speaks of Achitophel's rebellion and betrayal. In verse 14 it says: "Ve'atah enosh ke'erki alufi umeyuda'i" - a man of my own worth and stature, my mentor and my teacher, and also my close friend. And it continues: "Yachdav namtik sod" - together we would sweeten counsel, that is, together we would sweeten the secrets of Torah, and from here comes the derashah that one must learn together and not alone. This is the first lesson brought in Berachos.
What follows is an important half a verse that we say when we enter the shul: "Beveis Elokim nehaleich beragesh" - in the house of God we would walk with feeling. "Regesh" has two plain meanings: either with the proper feelings, with awe and humility, or in good company, that one should not go alone. Most of the commentators, among them Rashi, understood that the intent is amid a multitude, in a group of people. In any case, from the fact that the verse deals with the two lessons David learned from Achitophel, while the preceding verse calls Achitophel "alufi umeyuda'i" (my mentor and my friend), it emerges that David viewed him as his teacher and leader and granted him extraordinary honor, even though he was an evil man.
In the words of the Mishnah: "Sheken matzinu b'David melech Yisrael shelo lamad me'Achitofel ela shnei devarim bilvad, u'kra'o rabbo alufo umeyuda'o, shene'emar: v'atah enosh k'erki alufi umeyuda'i" - for so we find with David, king of Israel, who learned only two things from Achitofel, and yet called him his teacher, his guide and his close friend, as it says: "And you, a man of my own rank, my guide and my close friend."
From here the Beraisa derives a kal vachomer: if David HaMelech, the greatest man of his generation and king of Israel, a righteous and remarkably holy person, who learned only two small things from Achitofel, nevertheless treated him with enormous honor and called him his teacher, his guide and his close friend - how much more so an ordinary person, who learns from a friend who is no towering figure like Achitofel, even a single thing, must treat the one who taught him with the honor he deserves.
How do we learn from two things to one thing?
David HaMelech did not settle for giving honor; he went far beyond that, for the sake of Heaven. He called him "my guide" and "a man of my own rank." This was not a minimal discharge of some generic obligation of honor, but extraordinary honor. Accordingly, for an ordinary person who teaches even one thing, ordinary honor suffices.
David HaMelech is David HaMelech, and Achitofel is Achitofel. We are not David HaMelech, and the people we learn from are not Achitofel the wicked. If despite such an enormous gap David gave honor, then with ordinary people it is all the more so.
Achitofel did not teach David verses or halachos, but only advice: do not learn alone, and do not enter the beis midrash improperly. These are not even technical matters of Torah, and even so David granted him such great honor. Certainly, then, teachers who teach us Torah are deserving of honor.
Why is a person deserving of honor?
The most fitting reason for honor and esteem is not a person's wealth, power or beauty, but his being a treasury of Torah, someone engaged in Torah study. The reason is that all the other qualities are external to a person:
Wealth: one who honors a person because of his wealth - that person may lose his fortune.
Position: one who honors a person because of his power - that person may leave his post.
Beauty: one who honors a person because of his beauty - that person may be harmed in a fire, Heaven forbid.
These things are not intrinsic and do not attach to the person directly. In contrast, when a person is engaged in Torah, the Torah changes him and becomes part of him and bound up with him. It emerges that one who honors a Torah scholar honors him for something that is intrinsic to him.
The Mishnah brings a proof from Scripture, and it is worth noting that these are two separate verses that are unconnected to one another: "Kavod chachamim yinchalu" - the wise will inherit honor and receive it; "u'temimim yinchalu tov" - the wholehearted and righteous will be the recipients of good, "v'ein tov ela Torah" - meaning that the "good" mentioned in the verse refers specifically to Torah, and that is what the wholehearted inherit.
And from where do we know that the word "good" refers to Torah? From another verse: "Ki lekach tov nasati lachem, Torasi al ta'azovu" - "For I have given you a good teaching; do not forsake My Torah." From the end of the verse it is proven that the Torah is called a "good teaching." Therefore "the wholehearted will inherit good" means that they inherit the Torah, and for this reason "the wise will inherit honor" - the wise, who are the ones holding on to Torah, are deserving of honor.
The relationship between the end of the Mishnah and its beginning:
Some understand that the first part of the Mishnah deals with someone who taught you Torah, while the end comes to teach something new: that even someone who never taught you anything, but who is himself a treasury of Torah and a giant in Torah, must be treated by you with honor for what he knows.
Rashi focuses on a different angle: honor for your teachers. A person may have a teacher who taught him secular studies or a trade, how to be a good plumber. Every person deserves honor, every child and every king. But the special honor the Mishnah is discussing is when someone teaches you something of eternal value, your ticket to eternity in the World to Come, and specifically Torah, as opposed to other kinds of learning. That is the focus of the second part: the wise, who hold on to the "good" that is Torah, are the ones who inherit honor and who are deserving of our honor.
In summary: We learned that one who learns even a single letter from his fellow must treat him with honor, and we examined the various explanations of "a single letter" as well as the question of whether this is an obligation or a measure of piety. We saw the precedent of King David, who learned only two things from Achitofel and yet called him "alufi um'yuda'i" - "my guide and my close friend" - and the three approaches to deriving from this that the same applies even to a single matter. Finally, it was explained that true honor is given specifically for Torah, because Torah is intrinsic to a person and not external to him, and therefore "kavod chachamim yinchalu" - "the wise shall inherit honor".