The Rambam states in Hilchos Melachim:
"In the future, Melech HaMashiach, the Messianic King, will arise and renew the Davidic dynasty, returning it to its initial sovereignty.... Anyone who does not believe in him or does not wait for his coming, denies not only [the statements] of the other prophets, but [those of] the Torah and Moshe, our teacher.
"The Torah testified to his coming, as the verse states, 'G-d will bring back your captivity ... Even if your diaspora is at the ends of the heavens, G-d will bring you [to the land].' These explicit words of the Torah include all the statements made by all the prophets.
"Mention is also made in the portion of Bilaam in which Bilaam prophesies [the coming of] two anointed kings: the first anointed king, David, who saved Israel from her oppressors; and the final anointed king who will arise from his descendants and save Israel [in the final days]...."
In the next law the Rambam goes on to say: "Similarly, in regard to the cities of refuge the verse states, 'When G-d will expand your borders ..., you must add three more cities.' This command was never fulfilled. Surely, G-d did not give this command in vain. [It must, perforce, refer to the times of Mashiach]."
What is missing in the proof-texts cited by the Rambam in the first law that impels him to bring an additional proof from the cities of refuge? Additionally, why does the Rambam divide these proofs into two separate laws?
In fact, the proof from the cities of refuge introduces something entirely novel. The commandment to add in the times of Mashiach an additional three cities of refuge makes the matter of Mashiach's arrival one of the conditions of the commandments of the Torah.
That is to say, although the future redemption is explicitly stated in the Torah and the Rambam includes belief in the redemption as one of the fundaments of the Torah, nevertheless this is not one of the commandments of the Torah, for we do not find the Torah commanding us to believe in the redemption. Merely, since the redemption is explicitly stated in the Torah, whoever fails to believe in it "denies the Torah." However, the commandment of the additional cities of refuge transforms the redemption into part of one of the Torah's commandments.
But what is so special about the redemption becoming a part of one of the Torah's commandments?
The force of a commandment is truly eternal. Thus the Rambam writes: "It is clearly and explicitly stated in the Torah that the mitzvos of the Torah endure eternally and forever. They are not subject to change, nor to reduction or addition." The Rambam reiterates this in Hilchos Melachim: "The main thrust of the matter is, that the Torah, its statutes and its laws are everlasting. We may not add to them or subtract from them."
Since redemption is part of the commandment of the cities of refuge, therefore just as the cities of refuge is a commandment and as such "endures forever and is not subject to change," so, too, is it impossible for any change to occur -- G-d forbid -- in the promised redemption through Mashiach.
In light of the above we will better understand the Rambam's phrasing regarding the three cities of refuge, namely, "G-d did not give this command in vain." The Rambam is underscoring that since the additional three cities of refuge at the time of Mashiach's arrival is a commandment, it necessarily follows that it is impossible for it to change, G-d forbid, for G-d's commandments endure forever.
With regard to a divine promise transmitted by a prophet there exist circumstances that might engender a change, e.g., punishments foretold that do not come to pass, either because of G-d's forbearing or because repentance was done and the iniquities were forgiven. Even when the prophesy is of glad tidings and will not change, still this does not mean that the promise itself is not subject to change, only that it will in actuality not change.
Regarding the eternality of Torah, however, we are dealing with an entity that totally transcends the aspect of change, it is impossible for it to change. For just as G-d is not subject to change, so too are His Torah and its commandments, which are an expression of His will and wisdom, not subject to change.
Thus, the promise of redemption foretold by the prophets, although even as prophecy they will assuredly come to pass, yet they fall under the heading of "prophecy" -- something that even when it will not change is still subject to change.
With redemption becoming part of a commandment of the Torah, it becomes part of Torah's eternality -- something that is not even subject to change.
Based on Likkutei Sichos, Vol. XXXIV, pp. 114-117.
