Answer:

King David refers to the Holy Temple as a sukkah. Thus, in merit of dwelling in our sukkah, the Tabernacle will be rebuilt.

The Lubavitcher Rebbe teaches that one who is eager for Moshiach will find allusions to the subject everywhere. The holiday of Sukkot provides fertile soil for this endeavor, as every aspect of the holiday has some reference to Moshiach's coming.

The Talmud writes that in the merit of keeping the holiday of Sukkot and binding the four species, we will see the coming of Moshiach and the rebuilding of the Third Holy Temple. What is the inner connection between these two commandments and Moshiach?

King David refers to the Holy Temple as a sukkah, as he writes in Psalms: "In Shalem his Tabernacle is set." Thus, in merit of dwelling in our sukkah, the Tabernacle will be rebuilt. The mitzvah of taking the four species is part of the commandment of rejoicing on the holiday of Sukkot. Moshiach's name is Menachem, which means comfort, and he will bring joy and solace to the Jewish people.

The Lubavitcher Rebbe adds a deeper interpretation. The primary halachic element of the sukkah is the schach covering, made of branches. The covering takes on the holiness of the sukkah, and even after the holiday ends, it is forbidden to use the schach for any mundane purpose. The schach thus represents the act of transforming a physical part of the universe into something holy, from which the sacredness does not depart. This is the entire purpose of the Holy Temple, to take elements of the physical world and make them into an everlasting dwelling for G-d.