The Sages instituted numerous rabbinic decrees in order to prevent violations of Torah law. For example, the Sages extended the Torah’s prohibition of eating milk and meat together to include fowl, since it confused people who failed to distinguish between fowl and ‘real’ meat.
There are, however, a few cases in which the Sages went even further, and authored new positive mitzvot. The mitzvot to light Chanukah lights, to read Megillat Esther on Purim, to wash hands before eating bread - these are rabbinic enactments with no direct basis in Torah law. They are not extensions of Torah legislation or protective measures, but brand-new mitzvot. By what right could the Sages create them?
Even more audacious, the rabbis decreed that one recites a blessing when performing these rabbinic innovations: “Blessed are You, the Eternal our God... Who has commanded us to...” When did God command us to light Chanukah candles, or read the Megillah on Purim?
The Talmud in Shabbat 23a responds to this question. There are in fact two sources in the Torah for the rabbinic authority to establish new mitzvot:
Rav Kook explained that God-given commandments will naturally lead towards the goal of absolute good. This is understandable, as God knows the future and is aware of all implications of any decree. Man-made laws, on the other hand, even those designed by the most prescient legal scholars, will never be able to achieve the same results as a Divinely-decreed mitzvah.
Of course, the Talmudic Sages were blessed with ruach hakodesh, Divine inspiration, in addition to the logic and reasoning that are an integral aspect of the Oral Law. They used these gifts in order to attain results similar to God-given mitzvot, to further the cause of the Jewish people’s perfection in both spiritual and material realms.
The Sages examined two aspects when formulating a new law:
It is insufficient to take into account only immediate needs. If the people becomes estranged from its spiritual foundation, it has in fact become a different nation. Its unity and continuity are no longer assured.
Now we may understand why there are two sources authorizing the Sages to legislate new laws.
Regarding the need to address the current needs of society, the Torah commands: “Do not stray to the right or left from the word that [the high court] will declare to you.” This refers to decrees of the high court, which institutes legislation dictated by the state of the people, in order to uphold observance of the Sabbath, kashrut, and so on.
But other rabbinic enactments are new mitzvot, designed to maintain our ties with our spiritual heritage — such as lights on Chanukah, reading the Megillah on Purim, or washing hands before a meal, like the kohanim before they ate Terumah. Regarding the authority to enact these new mitzvot, the Torah states:
“Remember the days of old, reflect upon the years of each generation. Ask your father and he will tell you; question your elders, and they will respond.”
Israel’s past was elevated and holy, and is the source of our future success. “For His own nation remained God’s portion; Jacob is the lot of His heritage” (Deut. 32:9).
(Adapted from Ein Eyah on Shabbat 23a, vol. III, p. 73)