Before G-d was prepared to give His Torah to the Jewish people He first wanted to know whether they were prepared to accept it. With great enthusiasm the Jews expressed their desire to both accept and observe all of the laws of the Torah. Then according to Talmudic tradition (Shabbos 88a), G-d pressured the Jewish people to accept the Torah, and forced it upon them against their wishes.
The commentaries on the Talmud all wonder, why it was necessary to force the Torah upon the Jews if they had already enthusiastically expressed their willingness to accept it? The Medrash Tanchuma (to Parshas Noach) elaborates upon this aggada and distinguishes between the different parts of the Torah. The people were prepared to accept both G-d's written Torah, and all the halachos l'Moshe miSinai – transmitted directly from G-d. Their response to Moshe was that "kol asher deiber Hashem na'aseh" - that all that G-d had said we are prepared to accept. But the bulk of the Oral Torah is really what the Talmud and the Rambam refer to as "divrei Sofrim", halachos which were developed over the centuries with much rabbinic input. The rabbis were licensed to employ the various "middos shehaTorah nidrehses bohem" to read (so to speak) "in between the lines" of the Torah in order to present a fuller picture of each of the mitzvos. This the Jews at Har Sinai were not prepared to accept. They felt that this was not Divine! This is a human Torah, and all humans can err. Why should they agree to be subservient to the idea of other human beings? Who says that another is so much more intelligent than I? Each Jew should be entitled to interpret the law according to his own understanding!
And it was this part of the Torah that G-d had to force upon us. Whether we like it or not, G-d expects us to follow the positions set forth by the rabbis in interpreting the Torah. Not until years later, after the story of Purim occurred, did the Jewish people as a whole fully accept this aspect of rabbinic authority. It was at that time that Ezra and the Anshei Kneses Hag'dolah set up the entire system of the Torah sheb'al peh as we know it today. They formulated the text for all blessings and prayers, kiddush and havdalah, the system of thirty-nine categories of melacha, etc., along with many rabbinic enactments. Klal Yisroel at the period of the beginning of the second temple wholeheartedly accepted all of these formulations and innovations of their rabbonim.1
This is the significance of the expression we use (from the Rambam's formulation), that we believe (ani maamin) that the Torah as it is observed today, is an accurate transmission of that Divine Torah which was given to Moshe Rabbeinu. This added phrase, "as it is observed today", implies exactly this idea – to include all of those halachos where there was rabbinic input. We have "emunas chachomim". We believe that throughout all the generations there was an invisible Divine assistance given to the rabbis to develop the halacha in a correct fashion.
The Talmud (Menachos 29b) records an aggada that when G-d showed Moshe Rabbeinu a vision of the rabbis of future generations, Moshe became troubled with Rabbi Akiva. By the time of Rabbi Akiva, the halacha had already so developed, it seemed to Moshe as if this was not really the Torah he was given. Moshe was very upset over the distortion, until he heard a student ask Rabbi Akiva - what is the source of a certain halacha, and Rabbi Akiva responded that that was a "halacha leMoshe miSinai". In other words, all of the Torah, even in the days of Rabbi Akiva as well as today, is a legitimate development of Toras Moshe, based on the use of the "middos", and therefore everything is implicitly "included" in what was given to Moshe. He was given the text with the "middos", and when applying these "middos" to the text, all the details of the halacha as we know it today follow automatically. The "middos" simply guide that rabbis in their task of reading "in between the lines", in order to obtain a fuller picture of each mitzvah.
In the bracha one recites after an aliyah we praise G-d for having given us his Toras Emes, which is a reference to the text of the Torah shebichsav, as well as for having implanted in our midst ("nota besocheinu") the ability to further develop the "living" Torah ("chayei olam") with the aid of the "middos" and through rabbinic input (see Orach Chaim 149:10 and Gra nos. 27, 28). This bracha was composed after the period of the Anshei Kneses Hag'dolah, at which time Klal Yisroel came to realize – without any coercion – the immense value of the "divrei sofrim"; that the ability to have rabbinic input is what keeps the Torah in constant touch with an ever-changing world.2
Of course, the application of those "middos" is a science unto itself, which is only mastered by a small handful of qualified individuals in each generation. And the new additional halachos that read "in between the lines" have to "fit in" with "the spirit" of the rest of the Torah, which again can only be fully sensed by those few qualified individuals who have a proper sense of what "the spirit of the law" is!
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