Many people have written on this subject, both in books and online. This article will not add anything new to what they have written, but since so many people write me about this subject, evidently this article needs to be here at this site as well.
The Prophets have written a great deal about what the Messiah will do when he comes. Likewise, the Oral Torah has much to say about this as well, of course. Numerous Rabbis or the post-Talmudic era have collected these teachings and written about them. I shall write some of what has been written by the Rabbis. I hope and plan to quote many of the verses from Tanach (Jewish Bible) in a separate article one of these days. (To write in detail all the Talmudic and Midrashic passages would be too much for me to do.)
The Messiah will be a human being, the child of two human parents. He will be by unbroken patrilineal descent the undisputed heir of King David.
The Messiah will be the unchallenged king of all Jews everywhere in the world. (When I say unchallenged, I mean that none of the Jews will challenge him, once it is understood who he is. There is little doubt in my mind that the Catholic Church -- and perhaps many Protestant Churches as well -- will challenge him, and call him the "antichrist." But they will soon realize their error, because they will have no power against the true and only Messiah.) He will be anointed with the special anointing oil that the Prophets used when appointing kings. The word "messiah" is Hebrew for "annointed."
The King Messiah will reinstate the royal dynasty of David to its ancestral regal status. He will be king, and his son will be king after him. The King Messiah will live a very long life. When he dies, his son will become king. When his son dies, also after a long life, the grandson will be king after him. After the grandson's reign, this world will come to an end. The world will be dormant for one thousand years, and then the World to Come will begin and last for all eternity. We will be resurrected, which means that our souls will return to our bodies, and we will live forever on this, earth, which will also be renewed.
The King Messiah will be very active in the Holy Temple. He will reinstate the Sanhedrin, our highest court, and they will reinstate the High Priest. Together, they will rebuild the Holy Temple. It is possible that the Messiah will not be anointed king until after the Holy Temple has been rebuilt, but in any case from the beginning he will lead all the Jews.
Sacrifices will once again be brought at the Holy Temple.
The Messiah will lead us in war to defend us when enemies of the Jews begin the War of Gog and Magog. The enemies of the Jews will attempt to destroy us, as they have been attempting to do for millennia, but they will not succeed. Nevertheless, great destruction will take place, unless everyone repents first. If everyone repents, the War of Gog and Magog will not take place.
The King Messiah will gather the scattered Jews from all over the world. The lost Ten Tribes of Israel will be restored to the Kingdom of Israel, and the King Messiah will rule all twelve Tribes. He will also restore the family systems within each Tribe as they had originally functioned.
The King Messiah and the Sanhedrin will restore the Sabbatical system and the Jubilee (which involve seven-year counts and a fifty-year count), as well as all other Commandments that we are unable to fulfill today. He will uphold and restore complete performance of the commandments and complete obedience to Hashem and His Torah. He will cause all Jews in the entire world to fulfill the Commandments of the Torah, and to uphold and strengthen the one and only true Judaism. Likewise, he will succeed in getting all the nations of the world, everyone alive, to acknowledge and serve the One True G-d, Hashem. This does not mean that they will convert and become Jews. It means that they will keep the Seven Laws that Hashem commanded the children of Noah.
The Messiah will not cause any changes in the Commandments, nor will he add to them or subtract from them. He will certainly not start a new religion, nor will his followers start a new religion.
The Messiah will regain the entire Land of Israel for the Jews, and the boundaries of the land will be as great as those promised to Abraham.
The King Messiah will be extremely learned in Torah and absolutely observant of all the Commandments as taught and explained in the Oral and Written Torah.
There will be utter peace in the world. After the King Messiah has been victorious, not a single nation will dare consider waging war, and no nation will rule over any other. People won't even study warfare or battle tactics anymore. And no one will have any reason to fear anyone else, ever again. There will be no racism or other forms of oppression, ever again.
The nations will send their emissaries to the King Messiah, and the King Messiah will teach the world how to live in peace, and how to want to live in peace. Then, everyone in the world will enjoy eternal peace, for as long as this world will last. The great Rabbi, Rav Shlomoh Freifeld, of blessed memory, said in a talk he once gave that I attended that the Messiah will be a great teacher.
Good things will be easily available to everyone. When the Messianic Era comes, there will be no poverty, no war, no hardships, no reason for jealousy or competition, and no boredom. Everything anyone needs will be easily and quickly available, so that good things will seem to grow on trees.
Our primary concern will be in growing more and more spiritual, and we will all enjoy doing this.
The Messiah will not need to perform any miracles to prove who he is. Nor would the miracles be very significant. The Messiah's purpose is to bring about the return of the Jews from exile, to restore our united practice of the Commandments of the Torah, to raise our conciousness to a high level of fear and love of Hashem, and to reinstate the Jewish kingdom in the Holy Land of Israel as Hashem originally established it under King David. Those are the Messiah's essential purposes. Even bringing peace and affluence to the world will be only so that the world will be able to peacefully pursue our purpose of serving Hashem through Torah study and prayer -- Jews as Jews, and Gentiles as Gentiles. Performing miracles is not particularly meaningful, since the Messiah will be an obviously righteous man, and the Torah commands us to obey the righteous.
What I'm driving at here is that all the miracles in the universe do not make someone Messiah, if he is not righteous. jesus, who contradicted the Torah, could not have been the Messiah, no matter how many miracles they claim he performed. The real Messiah, when he comes, may or may not perform miracles, but he will certainly not contradict the Torah in any way, shape or form.
The King Messiah may decide not to perform overt miracles, but he will nevertheless be immediately recognized as a man who can judge the inner essence and spirituality of people. His wisdom will be recognized by all, and many representatives of all the nations will also come to learn wisdom from him and get his advice.
And no one in the universe will have any doubt that the Messiah has come, and we won't have to argue with people about whether or not the Messiah has come. There will no longer be any missionaries, and no one will be teaching anyone else about any other religions, except maybe as history.
Everyone in the world will see the prophecies fulfilled, and there will be no doubts about any of it.
In every generation, the potential exists for the Messiah to come. The Torah says, in speaking of the coming of the Messiah, "In its time I will bring it quickly" (Isaiah 60:21). The Talmud explains that there are two ways the Messiah can come. Hashem has established a final time, a deadline. If we repent, the Messiah will come quickly, before the deadline. If we do not repent, the Messiah will nevertheless come at the deadline (Sanhedrin 98a).
If we merit it, the Redemption will come quickly, and we will see many open and overt miracles.
If we do not merit the Redemption when the deadline comes, if we have not repented by then,it will happen in stages. It will take longer to happen, and there will be no or few open miracles. And there will be war first. Hashem will cause a king as evil as Haman to pass laws against us, and he will oppress us until we repent. And to destroy us, he will set into motion the war of Gog and Magog, which you may have heard of under the inexplicable name of "Armageddon."
The great Chofetz Chayim, the leading Rabbi around a century ago, said that the war of Gog and Magog will take place in three stages. The first stage, he said, was World War One. He predicted that the second stage would be much worse, and he predicted the precise year of the beginning of World War Two.
But if we repent, the Messiah can come even now, right this very minute.
How is this possible? In each generation there is one (or more) righteous person who is worthy of being the Messiah, if the generation repents and the time is right for the Messiah to come. In every generation, since we have not all fully repented, the potential Messiah of each generation has lived his life, and passed away, as do all people, whether righteous or not, completely unaware that he would have been the Messiah.
Some people think that the greatest person, the most righteous person of each generation is the potential Messiah of that generation. Often, they base it on the person's notoriety. This is an error. Maimonides teaches that the Messiah can even be an unknown righteous person, a quiet, private person that not too many people know about. We make the mistake of thinking that we always know who the most righteous person of every generation is. But this is an error. The most righteous person could live in secret, doing what he must do privately and quietly. And we simple people are in any case not capable of judging who is more righteous than who, because we can't read minds and we don't know what's in anyone's hearts.
If we all repent, the potential Messiah of this generation will become the Messiah. Note that he is not yet the Messiah, and he was not born the Messiah. He was simply a very righteous person. He himself has no idea that he is the potential Messiah of that generation. Certainly, the people at large have no idea who the potential Messiah is.
If we make ourselves ready for the Messiah, Hashem will make the potential Messiah of the generation into the actual Messiah. Hashem will send the Spirit of Messiah that He created before He created the universe, and the potential Messiah of the generation will thereupon become the actual Messiah. The Messiah will then proceed to fulfill all the Prophecies that he is destined to fulfill.
Please understand something: Hashem loves and wants all of His children. He wants none to be left out when the Messiah comes. Hashem therefore wants all Jews to repent, and all of us brought into the Messianic Era. Just a few won't do, and even one left behind is too many. So we can't look at any particular group and expect their righteousness to bring the Messiah. Each and every one of us must work to improve ourselves.
Jewish Law requires us to pray that the redemption and the Messiah come soon, and to eagerly anticipate it happening. We must, each day, continue to pray and continue to hope that the Messiah will come, even though he did not come yesterday, and he did not come this morning.
For we know that the Messiah will come, because Hashem has promised that he will come.
May it be Hashem's will that we all merit the coming of the Messiah immediately, very soon, and may he come quickly.
To learn more about the Messianic Era, and also the World to Come, go to the "Life, the Afterlife, and the Soul Gateway." http://www.beingjewish.com/toshuv/real_messiah.html