This week's portion is Tzav and it falls on Shabbat Hagadol (The Big Shabbath), when it is traditional to talk about Pesah (Passover), rather than the parashat hashavua (the portion of the week). In this case, however, the week's reading relates to the coming hag (holiday), although not necessarily in an obvious way. The title is taken from the imperative form of the Hebrew verb, 'to command,' which has the same root as the noun for command, mitzvah, and is the first distinguishing word in the parashah.
It begins (Leviticus 6:1):
Hashem spoke to Moshe, saying "Command Aharon and his sons thus: This is the torat olah (the teaching about the burnt offering) ...
The Torah continues, discussing the precise technique to carry out this and other sacrifices. These details are, in some ways, analogous to the rules we follow for Passover. For many people, Pesah seems to elicit a great concern for ritual. Some who are casual about kashrut (Jewish dietary laws) the rest of the year are compulsive about cleaning out all the places in which crumbs might possibly have fallen. I had a conversation a few years ago with someone who went to work on the holiday (which is forbidden by Jewish Law), but insisted that nothing come into his house during Pesah that was not strictly kosher for Passover.
Some people work like a slave, concerned to obey a vast array of strictures in preparation for the hag. Indeed, some prepare in advance almost all the food they will need, because halakhah (Jewish Law) tells us that in case a tiny bit of hametz (forbidden food or ingredients on Passover) gets into food prepared in advance, we can disregard it, but food prepared during Pesah must be 100% hametz-free. The up side of this, of course, is that when they finally sit down to the seder, they can really experience a feeling of liberation; this process is a kind of re-enactment of the going-out from Mitzraim (Egypt, literally: the narrow places).
We hear the tzav, the command, to purify our houses and our hearts and a lot of us act on the command. But why? We put a great deal of effort into preparing to commemorate an event that may or may not have happened, brought about by a supernatural being whose existence many of us doubt.
I think it is a matter of belonging. Mordecai Kaplan, whose writings laid the foundation for the Reconstructionist movement, argued that belonging—meaning belonging to the Jewish people—comes first. Pesah is primarily a family affair, not a community event. We hold services on the hag, but it is not really a synagogue holiday in the way Rosh Hashanah and Yom Kippur are. It is not the stylized agricultural holiday that we encounter on Shavuot and Sukkot. It is not a regular occurrence like Shabbat.
It is a celebration centered on the home. We first belong to family, and only secondarily to the community. Most of us were involved in some aspect of Pesah preparation and participation as children, strengthening the link between the holiday and the people to whom we felt closest. It is a link that brings us back, year after year, either to family or to others whose similar affinity for Pesah makes them surrogate family.
It is my contention then, that it is this feeling of belonging that creates the sense of commandment. It starts with the family and expands to include the community. Pesah is perhaps the most extreme instance, but we also find it in our commitment to tzedakah (social justice work), our commitment to each other in times of joy and times of trouble. We do not have to believe in the supernatural to believe in the force of commandment.