The last day of Passover ("Acharon Shel Pesach") is particularly associated with Moshiach and the future redemption. The Haftarah (reading from the Prophets) for this day is from Isaiah 11, which describes the promised future era of universal peace and divine perfection. Rabbi Yisrael Baal Shem Tov instituted the custom of partaking of a "Moshiach's meal" on the afternoon of the last day of Passover; in addition to the matzah eaten at "Moshiach's meal", the Rebbes of Chabad added the custom of drinking four cups of wine, as in the seder held on Passover's first days.
Moshiach’s Seudah is intended to deepen our awareness of Moshiach and enable us to integrate it into our thinking processes. The twelfth article of Rambam’s thirteen principles of faith is “I believe with perfect faith in the coming of Moshiach. Even if he delays, I will wait every day for him to come.” Though all believing Jews accept this principle intellectually, for many the concept of Moshiach remains an abstraction. Partaking of Moshiach’s Seudah reinforces our belief in this principle, translating our awareness of Moshiach into a meal, a physical experience which leads us to associate this concept with our flesh and blood.
The Baal Shem Tov’s linking of our awareness of Moshiach to the physical is significant, because it prepares us for the revelations of the era of the redemption. In that era, the G‑dliness that is enclothed within the physical world will be overtly manifest. As the prophet Isaiah declared, “The glory of G‑d will be revealed, and all flesh will see it together.” At that time, “the glory of G‑d” will permeate even the physical aspects of the world—“all flesh.”