The Paschal offering in Egypt marked the beginning of the final stage of the Jews' redemption from their oppression. It subsequently became the focal point of the observance of Passover which, despite its absence today due to our lack of a Temple, is still commemorated in several ways at the Seder.
Passover and the Problem of Timing
The Pesah Sacrifice stands out from among all other sacrifices in several respects. The first unusual characteristic of the Pesah that is noteworthy is its timing. Holiday sacrifices are typically offered on the Yom Tov when they are supposed to be eaten. Not so the Qorban Pesah, which is carried out the day before the holiday of Passover.
(Indeed, the Torah assigns the name "Pesah" to the 14 of Nissan, the day we refer to as "Erev Pesah", and calls the 7-day holiday "Hag Hamatsot" instead of "Pesah". That is to say, the 14 of Nissan is treated as if it were a holiday in its own right that revolves around the offering of the Paschal sacrifice. We are indebted to Rabbinic parlance for the change in terminology. )
Furthermore, the Temple obeyed a general rule that forbade sacrifices from being offered in the late afternoon. No sacrifice was allowed to be brought after the fixed Afternoon Offering (Tamid) was completed. The regular communal offering was supposed to be the final sacrifice each day. Remarkably, the Qorban Pesah is governed by the opposite rule - it must be offered after the Tamid sacrifice on the 14th of Nissan!
The problem of timing is compounded by the laws regulating the consumption of the sacrifice. Although the Qorban Pesah is offered in the Temple on the calendar date of 14 Nissan, one is not permitted to eat of its meat until the nighttime, i.e., until the 15th of Nissan! This is quite unusual. As a rule, offerings are to be consumed as soon as possible. Different sacrifices have different halachic deadlines that specify the amount of time within which they must be eaten. However, we almost never find a sacrifice that is offered on one day for the purpose of a meal on the next day.
One more striking feature of the Qorban Pesah deserves mention. In ancient times, prior to the construction of the First Temple, individual and local altars were still allowed to be used for sacrifice. Only communal offerings had to be brought to the national altar that was housed in the Tabernacle. The Paschal Sacrifice, however, despite the fact that it was a personal offering, could not be completed at a local altar - it had to be offered at the national sanctuary. Indeed, the Torah tells us in Parashat Re'eh:
You may not slaughter the Passover Offering in one of your gates which the Lord, your God, gives you. Rather, to the place which the Lord, your God, will choose to rest His name - there shall you sacrifice the Passover in the evening; when the sun goes down, it is the Holiday of your exit from Egypt.
Ironically, though, once the 15th of Nissan rolls around and the issue of eating the Paschal lamb comes up, communal seders are prohibited, and individualism is the rule:
In one house it shall be eaten - do not bring any of the meat outside of the house...
The Qorban Pesah is not the only mysterious element of Passover. The prohibition of hametz is also formulated in a way that seems counterintuitive. The Torah explicitly forbids the consumption of hametz during the seven days of Passover. The Torah also tells us that the Passover sacrifice may not be offered "on hametz". Our Rabbis teach us that this means that hametz must be removed from our domains beginning with midday of the 14 of Nissan, i.e., Erev Pesah.
An obvious technical question thus presents itself. Why does the Torah formulate this as two distinct prohibitions, one for half a day on the 14 of Nissan, and one for a full seven days during Passover proper? Why not simply command us to abstain from hametz from midday on the 14 through the end of the 21st?
Exodus - National and Individual
In order to better understand the significance of the 14th and 15th of Nissan, respectively, we must consider the dual function of the Exodus experience. One objective of the offering of the Qorban Pesah was the constitution of a new nation dedicated to the service of Hashem. This was accomplished through the communal participation in the sacrifice "the entire community of the congregation of Israel shall do it." The fourteenth of Nissan is a day on which every individual Jew demonstrates his identification with the Jewish people and its mission. This is reflected most clearly in the fact that the Qorban Pesah, although a personal offering, must be brought in a national setting.
As important as the events of the 14th of Nissan were for establishing the unity of the Jewish nation, they were only one step in the process of creating a holy community. Every household had to implement the concepts of Pesah in its own framework and apply them to its function. This process was initiated through the consumption of the Qorban Pesah in the home. Through carrying the sacrificial meat from the national sanctuary to one's private domain, an individual showed his intention to bring the message of the offering into his personal life.
Indeed, the seven day holiday of Passover can actually be construed as our "response" to the fundamental lesson of the Qorban Pesah. Through the Paschal Sacrifice, we demonstrate our rejection of the materialism of idolatry and our commitment to a spiritual, transcendent purpose in life. This shift in thought should yield a commensurate shift in behavior - an abandonment of leavened bread, the bread of luxury, and its replacement with matsah, the bread of servitude. Our recognition of the metaphysical basis of existence leads us to spurn the pursuit of wealth and pleasure and to dedicate ourselves to the service of a higher objective - knowledge and imitation of the ways of God.
There is a beautiful proof for this idea in a curious verse in Parashat Re'eh which presents the law of the Paschal Sacrifice:
You shall not eat any hametz on it; seven days you shall eat on it matzot, the bread of affliction.
There is an obvious difficulty with this verse. We understand that hametz may not be eaten "on" the Paschal Offering. We also know that hametz is prohibited during the seven days of Passover. But why does the Torah say we should eat matsot "on" the Qorban Pesah for seven days? After the first night, the Paschal Sacrifice is gone!
In light of what we have already explained, the verse makes perfect sense. The seven day holiday of Passover is in fact integrally linked to the Paschal Sacrifice - it represents our response to the spiritual challenge that the Qorban Pesah lays at our feet. Thus, we are actually eating matsot "on" - that is, in the wake of, or by dint of - the Passover Offering, for seven days.
We can now appreciate why the Passover sacrifice had to be brought after the Tamid offering, not before. Although it is offered during the daytime of the 14th of Nissan, its ultimate goal is only realized in the evening, where its consumption becomes a fundamental part of the observance of the Festival of Matsot. The fact that the sacrificial procedure is delayed until the conclusion of the daily order of offerings shows that it is in fact not related to that order of offerings - it is tied to the upcoming night's festivities. The national offering of the Paschal Sacrifices on the 14th of Nissan sets up the theological framework for the observance of Passover in each and every Jewish household on Pesah night.
The difficulty we raised with regard to the prohibition of hametz can now also be resolved. The Passover Offering cannot be completed unless its owners have already divested themselves of hametz in anticipation of the Festival. This is over and above the requirement to avoid hametz during the seven day "Hag Hamatsot" that begins in the evening. Our separation from hametz on the 14th of Nissan demonstrates that, even before we offer the Qorban Pesah, we are already prepared to bring it into our homes on the Seder Night. Thus, through abstaining from hametz on the 14th of Nissan, we underscore the connection between the offering of the Qorban Pesah in the Temple and its function as the "stimulus", as it were, for the Holiday of Passover proper.
We should not overlook the subtle and elegant manner in which the Torah formulated the holiday of Pesah. The central event on Passover is the Seder, which, in contradistinction to most of our holiday observances (Shofar, Lulav, etc.), takes place at night. Nighttime has a dual identity in Jewish Law. From the perspective of Shabbat and Holidays, the evening precedes the morning - "and it was evening and it was morning, one day" - so our holy days always begin the 'night before' their calendar date. From the perspective of the Laws of Sacrifices, however, the daytime is viewed, in the conventional sense, as preceding the nighttime. Offerings brought on a given day are eaten or burned during the night that follows.
The Seder Night, then, embodies both facets of nighttime. It is simultaneously the "end" of the 14th of Nissan - the date of the Paschal Sacrifice - and the beginning of the 15th of Nissan, the first day of the Passover Holiday. The Pesah Offering is consumed at the conclusion of the 14th of Nissan from the vantage point of the Temple's regulations, while serving as a key component of the meal that marks the beginning of the Festival on the 15th. Hence, it is through the night of the Seder that Biblical "Passover" and the "Festival of Matsot" are linked!
Finally, we may now be in a position to understand why the Rabbis chose to refer to the "Festival of Matsot" as "Pesah", despite the fact that this contravenes Biblical usage. Through adopting this terminology, the Sages emphasize that "Hag Hamatsot" ultimately derives from "Pesah". The Jews' ideological commitment, reflected in the Paschal Sacrifice, generates the impetus for the lifestyle change adopted on the Festival of Unleavened Bread. This lifestyle change, in turn, is a manifestation of the Jews' dedication to internalizing the ideas represented by the Pesah Offering. Thus, in a very real way, the "Festival of Matsot" embodies the message of Passover in its fullest form.