The Talmud (Berachos 47b) describes the process of becoming a talmid chochom as consisting of three parts: One must be 1) koroh 2) v'shonah and 3) v'shimeish talmidei chachomin.
Koroh means that one must master Tanach, which we refer to as mikrah. Shonah refers to mastering Mishnayos which represents all of the halochos of the Torah sheb'al peh. However, just mastering tanach and all of Mishna is not sufficient; one who is not meshamesh talmidei chachomim is referred to by the Gemorrah (ibid) as an am ha'aretz. Torah sheb'al peh does not consist only of a body of halochos; the mesorah of the oral Torah transmits attitudes as well, and this is the meaning of shimush talmidei chachomim. If one applies himself diligently he can succeed in mastering all of the body of the halochos in the gemorrah in a matter of several years. But the Talmud (Avodah Zorah 5b) tells us that in order to absorb the attitudes that the Torah sheb'al peh transmits from generation to generation one requires forty years.
After forty years of teaching Am Yisroel after matan Torah, Moshe Rabbeinu states after all of these years, you finally understood what I am driving at ("V'lo nossan lochem Hashem lev loda'as v'einayim liros ad hayom hazeh" Devorim 29:3). The Chachomim derive from this possuk that one does not really succeed in absorbing the attitudes transmitted within the Torah sheb'al peh until after forty years. The dor hamidbor did not have to work for a living and had the luxury of learning for forty years from Moshe Rabbeinu. In our generation, people learn from a rebbe for several years and then get married, get a job, and raise a family. Nonetheless, if they will continue to learn for forty years according to the guidelines that they received from their rebbe then they will understand this aspect of the Torah sheb'al peh as well. The Talmud (Sotah 22a with Rashi) refers to those who have mastered Tanach and Mishna but are lacking the shimush talmidei chachomim and yet take it upon themselves to teach others as a "rosha orum", since they have the ability to quote biblical and talmudic sources and fool the public into believing that they are talmidei chachomim even though they really are not.
In recent years, some people who claim to be talmidei chachomim have introduced new religious practices. Some will have women read Megillas Rus on Shavuos or Megillas Esther on Purim for the whole community; others will have women get some of the aliyos, and yet others will have women recite Kabbolos Shabbos or Pesukei d'Zimrah. On one occasion when Rav Soloveitchik was consulted about women's prayer groups, he did not want to say that it was prohibited. However, after pointing to the expression in the Talmud "ein ruach chachomim nochoh heimenu" (see Kiddushin 17B) he said that Orthodox Jews should understand that the displeasure of the great talmidei chachomim of a given generation with a practice indicates that the practice in question is against the attitudes transmitted as part of the Torah sheb'al peh (See Sefer Mipininei Ha'rav p.82, #1) When someone pointed out to the Rov that some of the musmachim who had introduced some of these practices seemed to know how to learn, the Rov responded in a sharp tone that one who is koroh v'shonah v'lo shimeish talmidei chachomim is considered an am ha'aretz (ibid p.208, #7.) The attitudes of the Torah sheb'al peh are not only an essential part of Torah which must be transmitted by a rebbe to his talmidim, but are also a litmus test for evaluating the correctness of any new practice.
On several occasions when the Chazon Ish would issue a psak on a contemporary social issue, and people would ask him where does it say this psak; where did you get that from? He would point with his index finger to his heart and respond, "it is written over here" (from Pe'er Hador, the biography of the Chazon Ish.) Rashi in his commentary on the Chumash (Shemos 28:4) writes in one place, "Libi omer li" (see Nefesh Ha'rav page 43.) In Yiddish folklore the question is posed how can Rashi follow what his heart dictates to him; isn't doing so a violation of "v'lo so'suru a'charei l'vavchem - you may not follow the dictates of your heart"? The traditional answer is that for one who has fulfilled the instructions of Mishleh (3:3), "Kosveim al lu'ach l'becha - write the words of Torah on your heart" there is nothing wrong with following one's heart. But this process of engraving the Torah on one's heart is what takes forty years of continued learning according to the guidelines of one's rebbe.
We often hear people asking when one of the rabbonim of our generation issues a psak on a sensitive sh'aila with social implications, "where does it say that psak?" Are we Karaites and as such require that everything has to be written down on parchment or in a book!? We have a masorah of a tremendous Torah sheb'al peh which includes within it attitudes on everything. Honest talmidei chachomim who have not only mastered mikra and mishna but have also been meshamesh talmidei chachomim and have absorbed these attitudes are certainly entitled and obligated to express their opinion based on the masorah that they have received and absorbed.
We believe, as it says in the Torah, that man was created btzelem Elokim. The Torah instructed all of us "v'holachto b'drachov" (Devorim 28:9) to preserve that tzelem Elokim by developing middos, i.e. developing the middos which the Tanach uses to describe Hakodosh Boruch Hu. The navi Yeshaya describes Hakodosh Boruch Hu as "Keil mistater"(Yeshaya 45:15. See The Breaking of The Glass.) The Ribbono Shel Olam does such a good job at hiding and being inconspicuous that there are many atheists who think that He is not even there. The Rov pointed out that the midas hatzniyus of Hakodosh Boruch Hu, which comprises doing everything b'tzinah (in an inconspicuous fashion), which we are expected to adopt in our personal lives as part of the mitzvah of preserving our tzelem Elokim, is most difficult for Americans. In America people long for their "five minutes of fame" and to see their picture and name publicized; everybody goes for publicity and nothing is done b'tzinah.
The Torah tells us that the difference between man and woman is not only physiological, rather there is also a difference in the tzelem Elokim (see Beraishis 127 and Divrei HaRav page 244.) The Torah tells us that on rare occasions Hakodosh Boruch Hu felt it necessary to reveal himself. We too are called upon, on occasion, to do things b'farhesiya. For example, we have a chazzan who davens at the amud, somebody gets an aliyah, and we appoint a Rabbi to lead our community. The Chumash tells us, "Som tosim olecho melech" (Devorim 17:15), and the Torah sheb'al peh comments, "Melech v'lo malka". Even when it is necessary to compromise on our middas ha'tzniyut, the Halacha recommends that whenever possible a woman should not be called upon to be the one to compromise. True, strictly speaking, the Mishna tells us that a woman may get an aliyah, but the Talmud points out that this would constitute a violation of kovod ha'tzibbur, since it would imply that there were not enough literate men available to take care of the entire kriyas ha'Torah and as such we felt compelled to ask a woman to compromise on her tziniyut. Getting an aliyah or reading the Megillah in public is not, and should not be seen as, an entitlement, which one might then think that women should be equally entitled to. It is rather a necessary compromising of one's tzelem Elokim. As we mentioned above, this perspective is the diametric opposite of the attitude of contemporary American society.
From the time of ma'amad Har Sinai through the building of the second Beis Hamikdosh was the period of Torah sheb'chsav. The Seder Olam tells us that after the nivi'im acharonim passed away the Jewish people no longer had any prophecy, and from then on we had/have to pay close attention to what the chachomim tell us. This means that the end of nevuah marked the beginning of the period of Torah sheb'al peh. Indeed the Midrash comments (Vayikra Rabbah 7:3. See Bava Basra 8a), based on the posuk in the novi, that the future geulah will only take place in the zechus of the study of Mishnayos, i.e. the Torah sheb'al peh. During the entire period of the second Bais Hamikdosh, there was trouble from the Tzedukim (see B'ikvei Hatzon p. 139.) Ultimately, the Tzedukim disappeared and the traditions of the Torah sheb'al peh preserved the Jewish people.
Orthodox Judaism is a G-d centric religion dedicated to fulfilling Hakodosh Boruch Hu's will, not to injecting our own will into His Torah. There have been many groups over the course of Jewish history, from the Karaites and Tzedukim to today's deviationists, which were led by people who rejected the attitudes of the Torah sheb'al peh and catered to contemporary desires and fads. In each case these groups, with the passage of time, disappeared and their adherents were lost. By contrast, the Jews who absorbed and lived by the attitudes transmitted from generation to generation via shimush talmidei chachomim live on eternally through their Torah observant descendants[1].
The Shabbos prior to Rosh Hashonah is always Parshat Nitzovim. As the parsha says, we are called upon this time every year to enter anew into a covenant with Hakodosh Boruch Hu. We must recommit ourselves to the bris of the Torah sheb'al peh, with all that that implies, and in that merit may we be zocheh to the geulah.
[1] Ed. - see Straightening Out Our Priorities, where Rav Schachter further develops the idea of living on through our children.