One Shabbos morning the students came to the beis medrash for Shacharis and there was a strange looking fellow, obviously not a student, and obviously missing some of his marbles, putting on tefillin. It didn't seem that he simply had not realized that it was Shabbos, so we all stayed away from him. When Rav Dovid Lifshitz arrived, he walked over to the young man and spoke to him softly in Hebrew. He pointed out that today is Shabbos and tefillin are not worn. The young man responded that he knows that, but he had received a nevuah (a prophecy) that he should wear tefillin today, despite the fact that it was Shabbos! Reb Dovid was not phased by his reply. He simply continued the conversation and asked, "in what language was this nevuah"? The young man replied - in English. Whereupon Reb Dovid told him softly, "you must be mistaken. Nevuas are only given in Hebrew." Whereupon the young man thanked him for his clarification and he proceeded to remove his tefillin.
We were stunned watching all of this! You have to master abnormal psychology to be able to convince a meshugena that he's wrong. The possuk in Sefer Melochim (I:5:11) says that King Shlomo was blessed with wisdom, and was "wiser than any other person". The rabbis understand this to imply afilu min hashotim - that he was even wiser than the meshugaim!!
G-d gave His Torah and promised that he would supply us with prophets from time to time (Devorim 18:15) to guide us. When Maamad Har Sinai is described, the chumash says (Devorim 5:22) that Hashem spoke to the Jewish people in a loud booming voice, ("kol gadol") and He did not stop ("velo yasaf"). The rabbis (Shemos Rabba 28) understand this to refer to the fact that G-d continues to communicate to us both through the prophets as well as through the talmedei chachamim.
But not any old crackpot who sets himself up as a "novi" is to be listened to. Our tradition (see Rambam Hilchos Yesodei HaTorah chap. 7) has prerequisites that must be met before one qualifies to be recognized as a novi. Likewise our tradition has guidelines regarding the substance of the prophecy (ibid chap. 8 - 10). If one tells us that he has received a prophecy to permanently do away with any one of the mitzvos, or to worship avoda zarah even if only temporarily, we know that he is a false prophet.
Similarly there are guidelines regarding a rabbi rendering a halachic view. There is room for chiddush, but no room for shinui. One of the thirteen principles of our faith is that the Torah laws can not change. But at the same time the medrash tells us (see Yalkut Shimoni to Sefer Shoftim 5:8) that Hakadosh Baruch Hu cherishes chidushei Torah, and it is for that reason that the talmedei chachamim engage in milchamta shel (the battle of) Torah, in order to come up with such chidushim. It is a fine line that distinguishes between chiddush and shinui[1].
If a learned G-d fearing individual comes up with original insights by applying the middos (rules and regulations) shehaTorah nidreshes bohem which were transmitted by the Torah shebeal pe (oral Torah), then we have the right to assume G-s is still communicating with us via the psak of the rabbi. And the psak of the rabbi is binding because we believe that "G-d will reveal His secrets to those who fear him" (Tehillim 2:14, see Sotah 4b.)
When the Torah (Shemos 20:1) describes the proclamation of the ten commandments, the expression used is that "G-d spoke all of these words (kohl hadevorim)" and our tradition has is that the word kohl is referring to the fact that everything intelligent any future talmid chacham will come up with was implicitly included in the Torah that G-d gave us at Har Sinai.
When Rambam formulates what he considers to be the thirteen principles of our faith (commentary to Mishna, Sanhedrin Perek Chelek) he writes that not only do we believe that at one time(maamad har Sinai) G-d revealed Himself to us, and gave us His Torah, but also that the Torah as we observe it today is min hashomayim. There are individuals who consider themselves Orthodox who believe that at one time the Jewish people did have a Divine Torah, but the amoraim misunderstood the tannaim, the rishonim misunderstood the Talmud, and the achronim misunderstood the rishonim. "But don't get me wrong," they would say "- I'm Orthodox! And therefore I feel that the laws of the Shulchan Aruch are all binding, even though I think everything is in error." This is not the Orthodox position. If one is really convinced that a certain psak is really in error, he is not permitted to follow it[2]. To err is human, and a Shulchan Aruch which is full of mistakes is a man-made Torah as opposed to a Divine one. Rav Chaim of Volozhin was fond of signing off his teshuvos, "the G-d of truth gave us a Torah of truth, and our eyes are only focused on the truth."
We believe that G-d protects His Torah from errors. Any mistakes made over the years by poskim, will ultimately be corrected. The psak of the rabbis is binding because we have the right to assume that G-d has behind the scenes "revealed His secrets to those who fear him."
The story is told of the Rav Yechezkel Landau, author of the Sheilos uTeshuvos Nodah Beyehuda, that on one occasion he was presented with a "shaila" in hilchos treifos. After thinking for a few moments he insisted that the shaila was not real, that the organ of the animal must have been tampered with after the shechita. When the guilty baal habayis finally admitted to the charge, Rabbi Landau explained how he knew: for many years whenever he would pasken a shaila, he would have a very comfortable and confident feeling that from heaven they had assisted him to pasken correctly. On this occasion, even though he had formulated a clear-cut halachic opinion, he did not feel comfortable issuing his psak. He felt that on this occasion he was not receiving any Heavenly assistance, and he wondered why. He quickly came to the conclusion that Divine assistance not to err in psak is a miracle of sorts, and G-s is not in the practice of performing miracles unnecessarily. Obviously in this instance there was no need for any Heavenly assistance; the shaila was a fake!
I recently read a fascinating article encouraging the Conservative movement to adopt as its new slogan the slogan of some Christian group: "g-d is still speaking." The writer states that she is a Conservative Jew because she believes this to be true, that G-d is still speaking. And she concludes her essay with the complaint, "why do so many Conservative leaders seem too often to be listening only to what G-d said to generations past (Jewish Week, May 12, 2006, pg. 27).
This has always been the position of the Orthodox. That's where all of the chiddush always is. G-d is still speaking to us through the rabbis' further development of the Torah shebeal peh. But just as we only follow the instructions of a prophet if who he is and what he has to say are within certain bounds; so too the rabbis are entitled, and indeed encouraged, to be "mechadesh" if what they have to say is within the bounds of the middos of the Torah shebeal peh.
The mishna in Avos tells us that G-d created the entire world with ten pronouncements. The Chafetz Chaim pointed out (Sefer Chomas Hados, chap. 11) that rabbis of the Talmud felt that whatever was initially created directly by the word of G-d was stronger, healthier, and better than the offspring of that initial creation. Tradition has it (see Rashi to Breishis 1:21) that after mashiach will come, there will be a seudah for the tzadikkim, and the levyassan will be served. This refers to the original fish created by G-d's words. Although that fish will be preserved for over five thousand years it is assumed that it will be either tastier or healthier than any of its offspring, even though they will be fresher.
Similarly, the rabbis say (Berachos 34b) that at that meal for the tzadikkim, special wine will be served, made from the original grapes created (during the six days of creation) directly by the word of G-d. Wouldn't it make more sense to make some wine from freshly grown grapes? Obviously the rabbis' tradition was that those original grapes, created directly by the word of G-d, were clearly superior to any others.
The Talmud (Avoda Zarah 8a) transmits a tradition that Adam Harishon brought as a sacrifice that original ox created by the word of G-d. That animal was obviously considered "the choice", to be preferred over any of its offspring.
With respect to Torah, however, this is not the case. We do not consider those laws of the Torah directly dictated by G-d to Moshe Rebbeinu as more important than the laws developed by the rabbis of the later generations. King David says in Tehillim (119:72) that the Torah from G-d's mouth (tov li Toras picha) is to be preferred over thousands of gold or silver pieces. Does the Torah "from G-d's mouth" refer only to the text of the chumash dictated word for word and letter for letter by G-d? Rav Chaim of Volozhin pointed to the story related in Gittin (6b) that two amoraim expressed differing views regarding the Biblical story of the pilegesh begivah. Soon after, Rav Avyasar met Eliyahu Hanavi who told him that just then Hakadosh Baruch Hu was also learning that parsha in Sefer Shoftim, and He Himself said over the two suggestions of the two amoraim. Apparently, any honest intelligent chiddush which a later talmid chacham comes up with will also become "Toras picha" by virtue of the fact that Hakadosh Baruch Hu will say that over also.
[1] See Rav Soloveitchik's essay "The Halachic Mind", footnote 98
[2] It goes without saying that when evaluating a psak, one must factor in any discrepancy between his own knowledge and qualifications vs. those of the posek espousing the psak in question, and what such a discrepancy may indicate regarding which person is the one who is in error