The belief in the coming of Moshiach and the Messianic redemption is one of the fundamental principles of the Jewish faith.1 Every Jew must believe that Moshiach will arise and restore the Kingdom of David to its original state and sovereignty, rebuild the Bet Hamikdash (Holy Temple of Jerusalem), gather the dispersed of Israel, and in his days all the laws of the Torah shall be reinstituted as they had been aforetimes.2
Whoever does not believe in him, or whoever does not look forward to (and anticipate) his coming, denies not only [the words of] the other prophets but also [those of] the Torah [the Five Books of Moses] and of Moses our Teacher! For the Torah,3 testifies about him, as it is said: “G‑d, your G‑d, will return your captivity and have compassion on you. He will return and gather you.. If your dispersed be in the utmost end of the heavens.. G‑d will bring you..” (Deuteronomy 30:3-5) These words, explicitly stated in the compound all the things spoken by all the prophets.
Some authorities view this principle as an integral part of the first of the Ten Commandments (“I am G‑d, your G‑d, who has taken you out of the land of Egypt, from the house of bondage;” Exodus 20:2), which charges us with the belief in G‑d, i.e., “to know that He who created heaven and earth is the sole ruler above and below and in all four directions.. This includes.. [the principle] that man is asked in his judgment after death, ‘Did you long for salvation?’ The Scriptural source for this obligation is compounded in the above: just as we must believe that G‑d took us out of Egypt, as it is written, ‘I am G‑d, your G‑d, who has taken you out from the land of Egypt’ .. so I want that you believe that I am G‑d, your G‑d, who will yet gather you and save you..” 4
1. Rambam, Principles of the Faith, Article 12.
2. Rambam, Hilchot Melachim 11:1
3. Ibid. See below, ch. VII-A.
4. R. Yitzchak of Corbeil, Semak, par. 1. See below, ch. VII-A.