We are commanded by Hashem through MOSHE Rabbenu to heed the teachings of the Chachamim. Moshe says: LO TASUR MIN HADAVAR ASHER YAGIDU LECHA, “…you shall not deviate from the word they shall tell you…”. (Deut. 17,11) We make a Berachah whenever we perform a Mitzvah. The Halacha tells us that even for a Mitzvah of Chazal we have to make a Berachah.
The question raised by many is how can we say VETZIVANU that He has commanded us when in fact it is only a requirement of Chazal. The answer given to this question is that the Pasuk quoted above tells us to obey the dictates of Chazal; hence what they tell us to do is in fact sanctified by Hashem as is evident from this Pasuk.
Many people minimize the importance of Rabbinic Mitzvot. From this command in the Torah we see that the Rabbinic regulations are as obligatory on us to carry out as are the Mitzvot explicitly mentioned in the Torah.