Rabbi Hershel Schachter
The "Giving" of the Torah
In our tefillos we refer to Shavuos as zman mattan Toraseinu. Hashem gave us the Torah as a gift (a mattana). When one gives someone a gift, he no longer owns it and the recipient now becomes the "ba'al haboss". When Hashem "gave" us the Torah we became the baalei-battim. The Talmud relates (Temurah 16a) that after Moshe Rabbeinu passed away, several thousand halachos were forgotten. The people approached Yehoshua, as they had always approached Moshe Rabbeinu during the previous forty years, and requested that he ask Hashem what the correct halacha was. Yehoshua replied, "lo bashomayim hi", that the one and only navi who Hashem told halachos was Moshe Rabbeinu.
This idea is implied by the closing possuk both in Chumash Vayikra and Chumash Bamidbar. The Talmud (Megillah 2b, see Maharsha) understands the language of these pesukim to imply that only Moshe was given prophecy regarding matters of halacha. All other nevi'im are only told matters of hora'as sha'a (issues of a temporary nature, as opposed to halachos which are binding throughout all generations.)
This is the meaning of the seventh principle of faith (in Ramabm's listing of the thirteen ikarei ha'emunah) . The Zohar mentions that Moshe Rabbeinu represents Torah shebiksav, because he always received direct dictation from Hashem regarding all matters of halacha. This is why the chumash is referred to as "Toras Moshe" at the end of sefer Malachi, because everything was dictated to Moshe word for word and letter for letter. Moshe is therefore called "safra rabba d'Yisroel - the great scribe of the Jewish People. All other nevi'im and talmidei chachomim must figure out on their own the halacha. The Jewish people are the ba'alei battim over the Torah!
The Talmud (Bava Metziah 76a) relates that on one occasion there was a dispute between Hakadosh Baruch Hu and the angels regarding a certain matter of halacha. Because the Torah had been "given" to the Jewish people, they (Hashem and the angels) felt that the question must be submitted to a rabbi who was an expert in the field for a final decision. Rabbah sided with Hakadosh Baruch Hu (this was the last halachik decision he made before his death.) The Rambam (end of Hilchos Tzora'as) has not accepted Rabbah's view, and paskens against the Rebbono Shel Olam! Isn't that odd? The Kesef Mishna explains that this is based on lo bashomayim he. The Rebbono Shel Olam himself instructed us that revelations of His will outside the context of the mesorah we were given on Har Sinai are not relevant in determining the halacha l'doros. He made us the baalei battim over the Torah, and halachik issues must be decided by human talmedei chachomim.
We are only the baalei-battim over deciding Torah matters within the bounds of the middos she'ha'Torah nidreshes bohem. Even in the area of establishing the Jewish calendar (as well as kiddush hachodesh and ibur shana) where we have a principle that atem afilu mut'im - that even if the beis din declared Rosh Chodesh in error, their psak still stands - our control is only within certain bounds: no month can have less than twenty nine days of more than thirty days, and no year can have less than twelve or more than thirteen months.
Talmedei Chachomim should be aware of the great responsibility which was placed upon them when they were tasked with determining what the halacha should be. This awareness should result in their making halachic decisions with a proper degree of seriousness.
 See the end of the first chapter of Rav Yosef Dov Soloveitchik's hesped for his uncle Rav Yitschok Ze'ev Soloveitchik (Divrei Hagos V'ha'aracha p. 65 - 68)
 This is why the rabbis derive halachos from the fact that words in the chumash are written with an extra letter or missing a letter