In the first chapter of Maseches Avos, in Mishnah 16, we meet Rabban Gamliel. His figure stands out for several reasons. First, he is the first person whose name is accompanied by a title of honor: until now the Sages were mentioned by their given names alone - Shammai, Nittai, Hillel, Antigonus and the like - whereas here we find the title "Rabban".
The meaning of the title "Rabban":
"Rabban" means "our teacher". This title was reserved, more or less, for the Nesi'im after Hillel, the only exception being Rabban Yochanan ben Zakkai, who was also a sort of Nasi. Rabban Gamliel was the Nasi of the Jewish people after Hillel.
It is quite possible that Hillel had a son named Shimon, who served as an intermediate figure and held the position of Nasi as well, and who is not mentioned here. Shimon the son of Hillel had a son named Gamliel, and he is the Rabban Gamliel the Elder before us: Hillel's grandson, serving as Nasi, who lived in the time of the Beis HaMikdash.
The breaking of the chain of transmission:
Take note of the wording: "Rabban Gamliel used to say" - it was his practice to say. Something very important is missing here: until now a chain of transmission was being built, in which each Sage received from the one before him; and now Rabban Gamliel appears without any explicit mention of having received from those who preceded him.
The reason for this, as we mentioned in the previous section, is that we have entered the era of dispute - an era in which hundreds of disagreements exist, not only among the students themselves but even between the students and their teacher. One cannot say of a person that he received the Torah from his teacher when he disagrees with him, and from the moment questions and disputes arose, the pure chain of transmission was broken and is no more. In fact, no one else in the Mishnah will be described as receiving from his predecessor, with one exception: Rabban Yochanan ben Zakkai in the second chapter, who received from Hillel.
Rabban Gamliel was a student of Hillel, who was his grandfather, and this is what he says:
"Aseh lecha rav, v'histalek min hasafek, v'al tarbeh l'aser umados" - appoint a teacher for yourself; remove yourself from doubt and avoid it; and do not tithe excessively by estimation.
The Bartenura, and most of the Rishonim as well, explain that the Mishnah contains not three statements but only two:
"Aseh lecha rav v'histalek min hasafek" - appoint a teacher for yourself, so that you will remove yourself from doubt.
"V'al tarbeh l'aser umados" - do not tithe excessively based on estimation.
We will discuss the two statements one after the other.
"Aseh lecha rav":
This phrase has already appeared in our tractate: in mishnah 6, Yehoshua ben Perachyah said "Aseh lecha rav" - make for yourself a teacher. But there the intent was that a person should appoint for himself a rav who would serve as the source of his tradition, so that he would receive an unbroken chain and a coherent message; and one source is preferable to many, so that he holds a single unified tradition, without internal contradictions and without open questions. That is straightforward.
The "Aseh lecha rav" before us here is something else entirely: it refers to the person who will be one's guide in life - and not only one's halachic guide, but one's guide for the bigger picture. The wording of the mishnah is "aseh lecha", make for yourself: it is not enough that a person has the rabbi of his shul. It may very well be that this is exactly the right man, but the essential point is that it be someone who is your rav, meaning someone who understands you.
This is the essential point: a person can rid himself of a great deal of the uncertainty in his life when he has an advisor, a mentor and a rav who can guide him - someone who understands him and where he comes from, and who can answer his questions in the way that suits him in particular, and not because that is what is written in the books, black on white, as the official line.
A person is free to choose who that will be, but he has to open himself up to him and make sure that he genuinely understands him. Then, when a question arises that involves life's uncertainty - Should I take this job? Should I move to Israel? Should I marry this girl? Should I switch to a different shiur? - he has someone to talk it through with: a person he trusts and who understands him, and who can help him arrive at the decisions that are best for him. This is a very important matter.
It is worth considering how far this principle is actually applied in the various communities:
Among chassidim: they hold of this idea and take it very seriously.
In the American Orthodox community: the situation is not bad at all.
In the Israeli chareidi system: this is the system our children are growing up in, and it seems to miss the point somewhat. A bachur enters a yeshivah together with five hundred other bachurim, moves from yeshivah ketanah to yeshivah gedolah, and sees the rosh yeshivah only from a distance. He comes to the Mir and watches Rabbi Asher Arieli on a television screen in the stairwell - and is that his rav? Certainly not. That misses the point.
The rav of our mishnah is the one who can help a person be "mistalek min hasafek", to remove himself from doubt. This is the first thing Rabban Gamliel says, and this is its importance and its necessity.
"Ve'al tarbeh le'aser umadot":
The technical point before us is that produce grown in Eretz Yisrael requires tithing, and here we are speaking of the gift that goes to the Levi'im - a tenth of the crop. Says the mishnah: do not guess, but rather separate a precise amount. If you have a hundred se'ah of wheat, ten of them must go to the Levi; do not estimate how many se'ah you have and then give nine, ten or eleven based on an assessment, but measure exactly. That is the simple reading.
Yet this reading is odd, since Maseches Avos is not a halachic work and does not deal with technical details of halachah, whereas here we have a distinctly halachic matter. Therefore one must say one of two things: either this really is the topic, and it refers to a particular way of relating to halachah; or it is a broader hashkafah point, which does not necessarily concern the separation of tithes as such but rather every area of life - that a person's halachic life should not be conducted out of uncertainty and guesswork. Sometimes there is no choice, and sometimes a person is forced to make his best guess, and that is the nature of life.
And indeed, the wording of the mishnah is "al tarbeh" - do not do it often. It does not say that one may never tithe by estimation, but that one should make every effort to avoid it as much as possible and not do so frequently.
On the technical level: if your obligation is to give ten out of a hundred and you gave eleven, that eleventh was not obligated, and the tithe is not a proper tithe; and if you were supposed to give ten and you gave only nine, it turns out that you tithed only ninety percent, and ten percent remained untithed. This is a technical problem, and some learn the Mishnah this way.
But many explain the matter more broadly: with any halachic doubt and any halachic question that comes up in a person's life - do not simply guess, but if it is at all possible, be precise and measure things out:
Decide in advance how much matzah to distribute at the Seder, and make sure that each person receives a proper measure of matzah.
Find out where the techum runs in the neighborhood, rather than estimating roughly how far you may walk between the hills.
Take your halachic life seriously and demand as much precision as you can. From a hashkafic standpoint, such a Jew is someone who takes things seriously, and does not float along doing things that may be fine and may not be so fine. Do not be like that.
In summary: In this Mishnah we met for the first time Rabban Gamliel the Elder, the grandson of Hillel and the Nasi after him, and the title of honor "Rabban"; we noted the absence of the language of transmission in his teaching, which reflects the entry into the era of dispute and the breaking of the chain of transmission. The two matters in the Mishnah are "aseh lecha rav vehistalek min hasafek" - appointing a rav and personal guide who understands the person and helps him resolve the doubts of his life, and "al tarbeh le'aser umadot" - the demand for precision in a life of halachah, from the actual separation of tithes to a general attitude of seriousness and responsibility.