Did the great Jewish theologian Moses Maimonides say in his 13 Principles of Faith that there will be none greater than Moses? If so, what becomes of the expected Messiah who does some things that Moses couldn’t do like bringing the knowledge of the God of Israel to the whole Gentile world and ending all war and all that. Wouldn’t that make the Messiah greater than Moses?
Yes, Rabbi Moses Maimonides (the Rambam) established as one of the 13 Principles of Faith that no prophet will exceed the prophecy (!) of Moses (Moshe), so that no one could ever claim that he has come to change the Torah of Moshe or erase any of the commandments. On the other hand, he explains that the messiah (mashiach) is mainly a political and military figure like Bar Kochva, whom R. Akiva and all of the leading rabbis of his generation exclaimed that he could be the mashiach. R. Akiva, not Bar Kochva, was the leading spiritual and religious authority of his generation but the military and political leadership is a different role (Mlachim 11, 3). It is true that the Rambam says that Mashiach ben David will be wiser than Solomon and have prophecy almost (!) like that of Moses (Tshuva 9, 2), criterion which clearly didn’t apply to Bar Kochva. One explanation is that the Rambam is referring there (in Mlachim 11, 3), to Mashiach ben Yosef, the first national/military messiah (or, as the Vilna Gaon writes, that it may be a time period and not necessarily one individual named Mashiach ben Yosef). Modern history has strengthened and even proven this approach, where we have actually seen the national renaissance of the Jewish nation in our political and military return to the Land of Israel through the State of Israel, and the in-gathering of the exiles [statistically, within 6 years, the majority (!) of world Jewry will be back in Israel for the first time since the exile of the 10 tribes, about 2,700 years ago], as a time period, without an individual person named Mashiach ben Yosef, and at first, being a secular, non-religious State. This national stage precedes the more spiritual and religious leadership of Mashiach ben David who will clearly be a specific individual (and not just a time period), and a religious (not just national) leader almost (!) like Moshe. This is similar to a child’s development where he first learns to develop his physical needs and only afterwards, is capable of developing his more spiritual and moral functions. In addition, mankind is constantly evolving both technologically and spiritually. Moshe was the ideal leader in his time, but was not allowed to lead Israel into the Land, because Joshua was more suited to do so. Similarly the Mashiach has a unique modern role which could not have been played by Moshe nor Joshua.