The last day of Pesach is celebrated by eating a special, festive banquet called Moshiach's seudah, a custom initiated by the Baal Shem Tov. The connection between the last day of Pesach and Moshiach is explained by the Tzemach Tzedek: "The last day of Pesach is the conclusion of that which began on the first night of Pesach. The first night of Pesach is our festival commemorating our redemption from Egypt by the Holy One, Blessed be He. It was the first redemption, carried out through Moshe Rabbeinu, who was the first redeemer; it was the beginning. The last day of Pesach is our festival commemorating the final redemption, when the Holy One, Blessed be He, will redeem us from the last exile through our righteous Moshiach, who is the final redeemer. The first day of Pesach is Moshe Rabbeinu's festival; the last day of Pesach is Moshiach's festival."
Pesach is the festival which celebrates freedom. The first day celebrates the redemption from the first exile; the last day celebrates the future redemption from the final exile. The two are intimately connected, the beginning and end of one process with G-d in the future redemption showing wonders "as in the days of your exodus from Egypt."
That Moshiach's festival is celebrated specifically on the last day of Pesach is not merely because Moshiach will redeem us from the last exile. Being last has a significance beyond mere numerical order, for that which is last performs a unique function. When the Jews journeyed in the desert after leaving Egypt, they marched in a specific order, divided into four camps. The last to march was the camp of Dan, which is described by Torah as "ma'asaf l'chol hamachanos" - "gatherer of all the camps." Rashi explains this as meaning that "The tribe of Dan...would journey last, and whoever would lose anything, it would be restored to him."
The concept of "gatherer of all the camps" - restoring lost property and making sure that nothing is missing - may be applied to various situations. The Baal Shem Tov, for example, taught that just as the Jews in the desert made forty-two journeys before they reached their final destination, Eretz Yisroel, so there are forty-two journeys in each Jew's individual life. The birth of a person corresponds to the initial journey when the Jews left the land of Egypt, and at each stage of life a Jew is somewhere in the middle of one of the forty-two journeys he must experience before he enters the next world.
Not only a person's entire life, but also every individual service to G-d has various stages or "journeys." In particular, the conclusion of a specific service acts as the "gatherer of all the camps" - to make sure that nothing is missing from that service. Pesach, it was noted earlier, is associated with the concept of redemption, and our service on Pesach is correspondingly directed towards hastening the arrival of the final redemption. But even if service on Pesach was deficient, if opportunities were missed, not all is lost: the last day of Pesach acts as "gatherer of all the camps" for the entire festival. Just as the tribe of Dan restored lost articles to their owners, so the last day of Pesach provides a Jew with the opportunity to rectify omissions in the service of Pesach, and thereby regain what is rightfully his.
Because Pesach is associated with the redemption through Moshiach and the last day of Pesach is the finish to and completion of Pesach, the last day of Pesach accordingly emphasizes the coming of Moshiach.
The notion of "gatherer of all the camps" applies not only to each individual Jew's life and service, but also to Jewry in general. The forty-two journeys between leaving Egypt and entering Eretz Yisroel took place in the desert, the "wilderness of the nations," which is an allusion to the period of exile when Jews sojourn amongst the nations of the earth. The forty-two journeys in the desert served as the means wherewith Jews left the limitations of Egypt. Thus all the journeys undertaken until the Jews actually entered Eretz Yisroel may be viewed as part of the exodus from Egypt. So too with the journeys in the exile: until Jews merit the final redemption, they are still journeying to reach Eretz Yisroel. In every generation, Jews are somewhere in the middle of one of those forty-two journeys.
As in the journeys in the desert, there is a "gatherer of all the camps" in the generations-long journey of Jews to the Messianic Era. Our present generation is that of "the footsteps of Moshiach," the last generation of exile. It is the "gatherer of all the camps" of all generations of Jews.
That this generation of exile is the "gatherer of all the camps" of all generations is not just because it is the last. Exile is not just punishment for sin.
The mission of Jews is to elevate and refine this corporeal world, to reveal G-dliness and to transform the physical into a dwelling place for G-d. Dispersed throughout the world in exile, Jews have been given the opportunity and the means to carry out this mission in all parts of the world.
This has been the Jews' task throughout their history. "Gatherer of all the camps" in this context means that if any portion of that task is missing, it now can be rectified. Thus the era of "gatherer of all the camps" is the era when the world will have been fully refined and G-dliness revealed: the Era of Moshiach.
It is for this reason that it is our generation which is that of "the footsteps of Moshiach" and "gatherer of all the camps." For the service of Jews throughout the generations has been all but completed, and only the finishing touches - "gatherer of all the camps" - is needed. We stand ready and prepared to greet Moshiach.
Moshiach, of course, could have come in previous generations. The Talmud, for example, relates that at the destruction of the Beis HaMikdash, a cow lowed twice. The first time meant that the Beis HaMikdash was destroyed; the second time meant that Moshiach was born. In other words, the potential Moshiach was born immediately after the destruction and had the Jews merited it then, he would have been the actual Moshiach.
Although Moshiach could have come in previous generations, the future redemption nevertheless has a greater connection to our generation - just as the idea of Moshiach is emphasized on the last day of Pesach, although the whole of Pesach is associated with the future redemption. For both are the concept of "gatherer of all the camps" and we accordingly celebrate Moshiach's seudah specifically on the last day of Pesach.
There is still more to the connection between the last day of Pesach and Moshiach. The prophet Yechezkel describes the exodus from Egypt - which took place on the first day of Pesach - as the birth of the Jewish nation.
The last day of Pesach, the eighth day, is therefore the day of the circumcision, which is "the beginning of the entry of the holy soul." Moshiach is the yechidah - the most sublime level of the soul - of the Jewish people. Until the body of Jewry has undergone circumcision it is not whole; its holy soul is missing. Moreover, the Alter Rebbe writes, the highest level of circumcision will take place in the future, when "The L-rd will circumcise your heart."
The Haftorah read on the last day of Pesach is also connected with the Messianic Era. It states: "The wolf will lie down with the lamb...He will raise a banner for the return...the earth will be full of the knowledge of the L-rd." All of these verses refer to the Messianic Era.
Thus the relationship between the last day of Pesach and Moshiach. But why do we mark this relationship by eating a meal?
Belief in Moshiach is a cardinal tenet of the Jewish faith, enshrined as one of Rambam's thirteen principles of belief: "I believe with perfect faith in the coming of Moshiach; and although he may tarry, I will wait for him every day that he shall come." But abstract belief is not enough. Our intellectual awareness must be translated into concrete action - by eating of Moshiach's seudah. Moreover, the food from Moshiach's seudah becomes part of our flesh and blood, and our faith in, and yearning for Moshiach permeates not just the soul's faculties but also the physical body.
Moshiach's seudah was initiated by the Baal Shem Tov, and there is good reason why it was by him specifically. In a famous letter to his brother in law, R. Gershon of Kitov, the Baal Shem Tov tells of the time he experienced an elevation of the soul to the highest spheres. When he came to the abode of Moshiach, he asked, "When will the Master come?" to which Moshiach replied, "When your wellsprings shall spread forth to the outside." In other words, it is the Baal Shem Tov's teachings - Chassidus - which will bring Moshiach, and it is therefore particularly appropriate that it was the Baal Shem Tov who initiated Moshiach's seudah on the last day of Pesach.
In the time of the Baal Shem Tov, the principal element of the seudah was matzah. The Rebbe Rashab, fifth Rebbe of Chabad, added the custom of drinking four cups of wine. Matzah is poor man's bread, flat and tasteless. Wine, in contrast, not only possesses taste, but induces joy and delight, to the extent that our Sages say, "Shirah (song) is said only over wine."
Chabad Chassidus conveys the concepts of Chassidus, first propounded by the Baal Shem Tov, in an intellectual framework, enabling them to be understood by a person's Chochmah (wisdom), Binah (knowledge), and Da'as (understanding) - ChaBaD. And when a person understands something - in this case the concepts of Chassidus - he enjoys it that much more. Chabad, in other words, introduced "taste" and "delight" into Chassidic doctrines, which until then were accepted primarily on faith alone.
The four cups of wine also allude to the Messianic Age, for which the dissemination of Chassidus - especially Chabad Chassidus - is the preparation. The four cups symbolize: the four expressions of redemption; the four cups of retribution G-d will force the nations of the world to drink; the four cups of comfort G-d will bestow upon the Jews; the four letters of G-d's Name which will be revealed; the four general levels of repentance.
[Source: Sichah of the Lubavitcher Rebbe, Acharon Shel Pesach, 5742]