One of the Brachot we make over Neirot Chanukah is Asher Kidishanu B’Mitzvotav Vitzivanu LeHadlik Ner shel Chanukah, “that we are made holy through the Mitzvah (of Chanukah) and are commanded to light candles.” The Gemara in Shabbat (23a) asks how we could recite Vitzivanu, “that we were commanded”, if G-d never told us to light Chanukah candles and it is only a Mitzvah D’Rabbanan. One of the answers given as the source for saying Vitzivanu is the Issur of Lo Tasur, the prohibition of deviating from the words of the Rabbis. Why does the Gemara choose this Mitzvah D’Rabbanan as a specific example of Lo Tasur?
We may also ask two more questions about the Chanukah story. The Greeks prohibited the Jews from keeping Shabbat, Brit Mila, and declaring the Jewish month. Why should the Greeks prohibit something as arbitrary as declaring the Jewish month? Additionally, the Midrash (Breishit Raba 2:4) says that the Greeks had the Jews write Ein Lachem Chelek BeElokei Yisrael, “you have no part with G-d of the Jews,” on the horns of their oxen. Why would the Greeks have the Jews inscribe this statement on the horn of their oxen?
Rav Yaakov Chaim Goldvicht ZT”L answers that the Greeks realized that Judaism is based on the words of the Rabbis. In order to assimilate the Jews, the Greeks wanted to separate practicing the words of the Torah through Mitzvot and the academic learning of Torah. The way to do this was to limit the power of the Rabbis.
The main strength of the Rabbis comes from applying the Torah to everyday activities. The Gemara in Brachot (17a) says the main part of wisdom is repentance and good deeds - in order for Jews to keep the Torah, they must use it practically. G-d invested into the Rabbis the power to change the physical aspects in this world. A famous example of this is the story of Rabban Gamliel and Rab Yehoshua. Rabban Gamliel incorrectly calculated Rosh Chodesh Tishrei to be on a different day than Rabbi Yehoshua’s calculation. Rabban Gamliel then ordered Rabbi Yehoshua to appear before him with his walking stick and money bag on the day Rabbi Yehoshua believed to be Yom Kippur. Even though he still thought he was right, Rabbi Yehoshua did as he was told. This shows that the Rabbis have the right to interpret nature and define it, even if they are wrong in their calculations. Similarly, there is the famous concept of Lo Bashamim He, that the law is not decided in Heaven, but rather by Beit Din on earth.
This is why the Greeks sought to prohibit the declaration of the Jewish month. This announcement symbolizes the power of Bet Din over the physical world. They sought to annul this power and therefore prohibited this declaration. This also explains the reason for inscribing Ein Lachem Chelek BeElokei Yisrael on the horns of their oxen. The Greeks wanted to show the Jews that G-d has no control over nature and over the physical world, that He does not so much as control the actions of the oxen.
It is for this reason that the Gemara specifically brings Nerot Chanukah as an example of saying “Vitzivanu” for a Dirabanan. We are showing that the Greeks are wrong and that the ways of the Rabbis are correct. We are asserting the Rabbis right to change nature and to add Mitzvot as they see fit. Therefore, it is only fitting for us to recite Vitzivanu.