"Torah is greater than priesthood and kingship, for kingship is acquired with 30 qualities, priesthood is acquired with 24, whereas the Torah is acquired with 48 ways. These are: ... (26) making a fence for one's words, (27) not taking credit for oneself..."
(26) Making a "fence" for one's words: This expression means to limit in some way one's speech. (The term "fence" is often used by the Sages metaphorically, as a safeguard. See for example 3:17 (http://www.torah.org/learning/pirkei-avos/chapter3-17a.html).) The precise meaning and ramifications are not entirely clear, and the commentators offer a number of explanations.
Some commentators (Midrash Shmuel) understand this to be a general injunction to limit one's speech, as excessive talk leads to empty, if not sinful, speech. (See earlier, 1:17; http://www.torah.org/learning/pirkei-avos/chapter1-17.html.)
R. Samson Raphael Hirsch explains in a manner more pertinent to scholars: A scholar should not be too vocal or outspoken. Although he should be prepared to speak out against injustice and take what are usually unpopular stands for truth, he should not force his views upon others. He will preface his statements as being his own understanding of the matter. Likewise, the scholar should not cheapen his words by talking too much. His words should be limited and well-chosen; when he does speak, it should be worth listening to.
Another interpretation (Machzor Vitri, Ya'avetz) is that the scholar must safeguard his words from misinterpretation. His words must be clear and unambiguous. Being a person who studies Torah and teaches it to others, he must be aware of the impact his words have upon others. If his words are misheard or misinterpreted -- whether innocently or wantonly -- it will influence others and reflect on the Torah and Judaism accordingly.
In this regard, the scholar must see himself as somewhat of a public figure, under public scrutiny and ideally, one from whom others will learn. And of course, there are always those who are all too eager to find faults in leaders, especially religious ones -- perhaps in the interest of somehow justifying their own religious laxity. (Notice how focused the media always is over priestly misconduct (apart from society's general infatuation with such topics).) Rabbis, like political leaders, will always be quoted out of context and will have their words either naively or willfully misconstrued. (I'm sometimes amused after sending a class to be told by readers exactly what I said.) ;-) Thus, the scholar should be prepared to speak out firmly and unequivocally when necessary, but should ever be aware of the consequences of errors and the potentially malicious intent of his detractors.
It's interesting to note that this quality differs somewhat from many of the earlier ones of this mishna. Most of the earlier qualities dealt with how one becomes a scholar -- through study, careful listening, eschewing luxuries etc. Here we seem to have moved beyond "how-to" and begin dealing with practical rabbinics. No matter how wise and knowledgeable a scholar you are, it might all go to waste if you're not a good politician -- or at least a good public speaker.
The Talmud likewise states that a student may not render public decisions in Jewish law if he has not received authorization from his teacher (Sanhedrin 5b). The reason in part, explains the Talmud, is simply because some people just don't speak clearly and can be misheard or misunderstood. (The Talmud there proceeded to write some of the absurd laws which were promulgated on account of such miscommunications.) Thus, a scholar must "fence in" his words -- guarding himself both from innocent errors as well as willful misrepresentation. He must see himself as not only a scholar, but a spokesman -- and living embodiment -- of G-d's wisdom.
(27) Not taking credit for oneself: This quality is clearly imperative for the scholar, who must recognize that he is not G-d's great gift to the world but is merely doing his duty and at best living up to the potential G-d has granted him. This quality in fact was the subject of an earlier mishna in Pirkei Avos (2:9; http://www.torah.org/learning/pirkei-avos/chapter2-9.html), please see our discussion there.
It is also interesting to note the appropriateness of this quality after the previous. Once the scholar begins to become aware of his obligation towards others -- that he represents G-d's Torah and must keep in mind what others will learn from him, it is very easy for him to live for his image. The scholar now rightly sees himself as a public figure, a role model for Jew and Gentile alike. Well, it's very easy to get caught up in such a holy mission -- representing something bigger than oneself -- and just as easily forget what that mission is all about (almost regardless of how well you carry it out). The more I focus on my task of showing *you* the beauty of Torah, the less I remember to see it myself. Recent and past history is replete with people who fought hard and vicious for a holy cause and who became very unholy in the process.
Our mishna thus finds need to remind the scholar who he is and to place his mission in perspective. He is not out to save the world -- to make saints out of everyone else. He is fulfilling his own mission -- to G-d. He must constantly see himself as the humble servant following his Master's bidding. And then hopefully, upon seeing the truth and sincerity of his own mission, others will follow as well.