Even were the messiah to come today and say that the one true religion is Judaism and the one true path to the worship of the God of the Jews is exclusively by Talmudic principles, the first project the messiah (aka Moshiach) would do would not likely be the rebuilding of the Holy Temple. Here's some reasons...
- The Temple must be "a house of prayer for all peoples" (Isaiah 56.7). You can't assume that is likely if the very rebuilding of it starts a war. Yet, the rebuild is a sign of eternal peace. So effectively we need to wait for peace in the Middle-East before considering rebuilding the Temple, and then according to prophecy, the Temple will be a seal of eternal peace (according to both Jews and many Christians) when built out of the unity of goodwill that will exist in that time among nations.
- The rebuilding of the 2nd Temple in the time of Ezra and Nehemiah was not a universal success. Much of the Jewish people did not return to the Holy Land following that rebuild. We see from the order of the Scripture what went wrong. First the Temple was rebuilt by Zerubabel, then the Temple was dedicated and the Holy Word of the Lord was disseminated by Ezra, the Priest, and then Nehemiah fortified Jerusalem and pursued matters of peace and justice. It would seem likely that a reversal of this order must occur for a permanent peace to be ensured. First peace and justice must be administered, then the Holy Torah must be taught to those who would rebuild the Temple, so that everyone, and not merely a few, will wish to participate in giving honor to the Lord, and only then will everyone be united to such an extent that the whole world will be ready and desirous for the Holy Temple to be rebuilt.
- The people who must rebuild it, must be a united people, and on this issue there is currently no consensus among Jews. Thank God that there's going to be a messiah! But even if a messiah comes immediately, we are still probably talking several years before the world changes fast enough for all this to occur. According to Maimonides (Laws of Kings) no miraculous changes will occur in the world in the messianic age except that no nations will threaten Israel anymore. And if you think about it, God has built an intricate and delicate framework of free will into this world and after all that effort it is unlikely for that to be utterly thrown away overnight, though not impossible. Nachmonidies based on the prophecies of old forecasted an age of open miracles, which obviously would hasten the building of the Temple far beyond what anyone can calculate.