One of the most important activities that is part of the traditional preparation for Passover is the elimination of anything that has leaven in it (Hebrew: hametz). Why is this so important? According to the Torah, the Israelites did not eat leavened bread because they did not have time to bake it on their way out of Egypt (Exodus 12:34; Deuteronomy 16:3-4) and so it is prohibited as part of reenacting the Exodus every Passover. But this historical explanation only deals with the surface of the prohibition of leaven. In the laws of sacrifice at the beginning of the book of Leviticus (Leviticus 2:1-16; 6:7-16) there is one sacrifice which is made from semolina wheat: the minha offering. All forms of this offering must also not be leavened and so there is a significant connection in these laws to the upcoming holiday of Passover.
The grain offering may be baked, roasted on a griddle or fried in a pan. Despite the way the offering is prepared, it must be unleavened (matzah) and thus contain no se'or (sour dough yeast) or it is leavened bread. Leavened bread is for normal human consumption but only matzah can be used on the altar of the Tabernacle/Temple as an offering to God. However, during Passover, even the human community must eat only matzah and must eliminate all leaven from its habitations (Exodus 12:15).
And so while there are many issues in these laws that call out for explanation and investigation, the most obvious one is: Why is leaven banned in the Tabernacle/Temple at all times and also during the week of Passover? A deeper explanation connects both of these practices.
The late Bible scholar Jacob Milgrom, in his commentary to Leviticus, explained that "Fermentation is equivalent to decay and corruption and for this reason is prohibited on the altar..." Leaven is a symbol of both death and life in that it smells like death and yet produces the growth of the bread or the beer or the wine. While it is acceptable for people to eat leaven during normal times, it is prohibited on the altar as an offering to God because God is life itself and death cannot be in God's sanctuary. Thus leaven is not fit for sacrifice.
This means that during the week of Passover every Israelite home and the entire Land of Israel itself became one great altar to God, all without hametz. As a spiritual practice, abstaining from leaven for one week allows us, in this symbolic system, to attain a ritually higher state of connection to God.
As Bible scholar William Propp also points out, the removal of leaven has still deeper meaning:
Yeast is in theory immortal. The Israelite chronometric system, however, and their entire world-view presuppose that time is not a continuous stream. It is and must be periodically interrupted... [e.g. he Sabbath, Sabbatical Year, and the Jubilee] The laws of unleavened bread ensure that the bread by which people live does not transcend time, at least within the Holy Land. Once a year, all yeast must be killed, with a week of separation before the souring of a new batch...Leaven symbolizes the undesirable: misfortune, evil intensions and especially ritual impurity. To purge it is to make a fresh start, to experience catharsis. This understanding fits well with the historical context of the holiday. In the month of the New Grain, the Hebrews cast off centuries of oppression and assumed a holier, more ascetic status for their desert wanderings and subsequent national life. (Anchor Bible Commentary to Exodus 1-18, p. 434)
Jewish commentators though out the ages have interpreted hametz in a similar fashion. Philo of Alexandria the Jewish philosopher (20 B.C.E.-50 C.E.) interpreted the prohibition of leaven to the idea that during Passover we must return to a more natural state of living since leavening is a product of human art (or techne in Greek from where we get our word technology) or rather the human manipulation of the natural world:
The interpreters of the holy scriptures do also say that the unleavened food is a gift of nature, but that leavened bread is a work of art. Since, therefore, the vernal festival (Passover) is a commemoration of the creation of the world, and since that it was inevitable that the most ancient persons, those formed out of the earth, must have used the gifts of the world without alteration ... the lawgiver ordained that food which was the most suitable to the occasion, wishing to kindle every year a desire to walk in the paths of a holy and rigid way of Life ... For they are all unleavened, the clearest example of an unmixed food which has been prepared not by human skill for pleasure but by nature for the most essential use. (The Special Laws 2:159-160)
In the New Testament, Paul uses the metaphor of leaven (I Corinthians 5:7-8) as a homiletical device to talk about the need for spiritual and moral removal. His use of this metaphor shows that his audience was well-versed in this ancient Jewish interpretation.
And in rabbinic literature, leaven is often used as a metaphor for the evil inclination or yetzer ha-ra (Babylonian Talmud, Berakhot 17a).
Preparing for Passover then is not only about removing the physical leaven from our homes but also about the spiritual of the law: The cleaning out of our homes should also be a cleansing of our spirits, a renewal to the meaning of our Exodus experience and the new Creation that is spring.
The original version of this article was published in The Jewish Standard.