I read in several places that customs acquire the status of Law and are binding on later generations, and that this is true even in cases when the original reason for the custom is no longer valid. For example, we still celebrate an extra day in the holidays in the diaspora despite the fact that dates are no longer uncertain, and haven’t been uncertain since the calendar was codified over fifteen centuries ago.Why is that? When G-d tells us to do something, as in the written and oral Torah, it is the all knowing ruler of the universe. He knows exactly in what circumstances it will be applied, and what its effects will be. People, such as the sages who decided Kitniyot (legumes) are forbidden on Passover (only for Ashkenazik Jews) or the sages who decided to have a second day on the holidays in the diaspora, do not have that knowledge.

Thanks for your question. It is important to set the parameters before we launch into a discussion of the why’s and how’s of specific Jewish laws. There are 3 categories of Jewish law that you mentioned. There is minhag – custom, halacha d’rabanan – rabbinic law, and halacha d’oraysa – Torah law.

In terms of the practical application as it pertains to us – rabbinic and Torah law are the same – unless there are factors that do not allow us to perform all of the laws appropriately and therefore, force us to choose or modify which laws we can and can’t do. If we have to choose between a rabbinic or Torah law – we choose the Torah law always. If we have to choose between a custom and a rabbinic law – we choose the rabbinic law. Hashem gave us our written law (Torah) and oral law (Talmud – through Moshe, transmitted orally until written down in the Talmud). The rabbis put fences around or add to those laws in order to ensure proper adherence with our law.

With that said, a custom is also very important. We have a concept that “a custom of our fathers is in our hands” meaning that customs that are created for one reason and that reason is seemingly no longer valid are still upheld because our sages teach us that even though there might be a physical reason to do something today that makes a change in the spiritual world as well, as does every physical action that we take. When that happens there is now a spiritual value to that action that exists regardless of the original physical reason that a custom was started. Everything we do has a physical manifestation and a spiritual value. They go hand in hand and are both valuable. Without performing the physical action one can never tap into the spiritual world. Just the same, without the spiritual value of what we do our actions are meaningless.

I hope that this explanation gives you some idea of why all aspects of Jewish life are so important. If you stil have any further questions about specific laws please do not hesitate to write back.

Thank You,
Rabbi Litt