As is well known, our tradition places great importance on proper speech. While we generally view this as a moral imperative -- avoiding unnecessary negative comments about others, gossip, and slander -- it is also a necessary ingredient for proficiency in Torah study.
"Rav Yehuda said in the name of Rav: The people of Yehuda who were careful with their speech, the Torah was sustained in their hands; the people of Galil who were not careful in their speech, the Torah was not preserved in their hands" (Eiruvin 53a). The Gemara is perplexed as to the relationship between careful speech and the ability to achieve success in the study of Torah. The Gemara explains that the people of Yehuda were exacting in their speech, insisting on precision and clarity; whereas the people of the Galil spoke in ways that were not always readily understandable.
Most understand that in the world of science, precision is crucial, and a minor glitch can cause major problems and worse. Fewer seem to understand that such is true in the world of Torah. Great knowledge is no guarantee of the ability to transmit Torah. How we say something can be just as important as what we say. It is noteworthy that one of the requirements of ordination is that one speak clearly (Sanhedrin 5b). One who cannot do so should not be teaching, and should have his application to rabbinical school declined.
The Gemara links this precision with another trait, that of "giving signs", or what we may call mnemonic devices. In an era before books were readily available, one in which Torah was taught orally, having the ability to easily recall that which one had learned was crucial. "Making signs" would, no doubt, help one to remember that which he has learned.
The Gemara gives a second reason for the higher level of Torah retention in Yehuda. "The people of Yehuda learned from one teacher...the people of the Galil did not learn from one teacher". As Rashi explains, even if the teachers taught the same material, a student hearing it from two different teachers may get confused: "Even though the two of them are the same, the differences in language confuses and makes one forget". Torah preservation requires we have one mentor.
The Gemara then offers a third explanation: that the people in Yehuda, in contrast to those in the Galil, were "galu masechta". Rashi, apparently sensitive to the literal translation, (reveal a tractate), explains that the people of Yehuda taught Torah to others.
It is not uncommon for students, especially budding scholars, to feel that teaching others is a waste of valuable time that could be better spent learning more themselves. This is a tragic mistake. The mitzvah of Talmud Torah is primarily one of teaching others; "and you shall teach them to your children" is the source for the mitzvah of Talmud Torah (Kiddushin 29b). Moshe is Moshe Rabbeinu because he is the teacher par excellence. Learning Torah to benefit oneself only is, in many ways, a selfish act and lessens the value of the mitzvah. As anyone who has ever taught Torah can attest, teaching is the best form of learning: "I have learned the most from my students" (Ta'anit 7a).
Only those who can teach others can truly be said to understand what they have learned. When a student says he understands something, but can't explain it to others, that is a sure sign that he really does not understand it.
Rashi offers a second explanation, that galu masechta means to "explain that which they heard and are precise in the reasons for something, until their heart is at rest". If one wants Torah to have permanence, it is not enough to be able to properly explain something; one must also understand the reasoning behind any given position. One must not just parrot others, but must fully internalize its meaning and reasoning. We must be both intellectually and emotionally invested in Torah, so that it can speak both to our brains and to our hearts.
 During the Talmudic period the land of Israel was divided into 3 provinces; Galil in the north, Yehuda in the centre, and Transjordan to the east.
 In my first year at Yeshiva University, one of the core requirements was that of speech, where we were taught the fine points of speaking; a requirement that is unheard of in Canada. While the course was required by the college, it is clear that such a course must be a prerequisite for semicha.