If I say this three times a day, am I supposed to move to Israel?
The blessing asks God to do the gathering: "gather us together quickly from the four corners of the earth." Whether a person must live in the Land of Israel today is a separate question, and the old sources disagree.
Some are strong. The Gemara says a person should always live in the Land of Israel, even in a city that is mostly non-Jewish, and not outside it, even in a city that is mostly Jewish. The Sifrei (an early collection of teachings on the book of Devarim) tells of four sages who, while leaving the Land, cried and tore their clothes, and said that living there equals all the other commandments.
The Rambam (Maimonides, a 12th-century scholar who wrote a full code of Jewish law) allows leaving the Land for a while to study Torah, marry, or do business. He forbids settling outside it unless there is a severe famine or no way to earn a living, and even then calls it less than pious.
Others are more careful. In the Gemara, Rav Yehuda (a Babylonian sage) says that anyone who goes up from Babylonia to the Land of Israel breaks a commandment, reading Yirmiyahu (Jeremiah) to mean the exiles must stay there until God calls them back. His student Rabbi Zeira, who wanted to go, said that verse is about the Temple's vessels. He read an oath in Shir HaShirim (Song of Songs) as meaning only that Jews must not go up "as a wall," all at once.
So the sources split on the duty. They do not split on the hope: the Rambam lists gathering the dispersed among the Messiah's tasks, and says the Torah already promises it. Any duty to live there comes from other texts, not from this blessing.
Ketubot 110b-111a,Sifrei Devarim 80,Rambam, Laws of Kings 5:9 and 11:1,Devarim 30:3-4Who are the "lost" ones in the verse, and are they coming back?
The first line of this blessing comes from Yeshayahu 27:13 (Yeshayahu is Isaiah, a prophet from the time of the First Temple). A great shofar sounds, and "those who were lost in the land of Assyria" come to bow down in Jerusalem.
Who was lost in Assyria? The Radak (Rabbi David Kimchi, a medieval Bible commentator) says it means the tribes the king of Assyria exiled across the river. They were as if lost, he says, because they never came out again, unlike Yehuda and Binyamin, who returned after seventy years. The book of Melachim II (Kings) says the king of Assyria captured Shomron (Samaria) and exiled Israel to Assyria (Melachim II 17:6).
The Mishnah (the earliest written collection of rabbinic law, about 1,800 years old) records an argument about them. Rabbi Akiva (one of the great sages of that time) says the ten tribes will not return. They are like a day that goes and never comes back. Rabbi Eliezer says they are like a day that grows dark and then light again.
The Gemara then brings a teaching about whether the ten tribes have a share in the World to Come. Rabbi Akiva says no. Rabbi Yehuda HaNasi (the editor of the Mishnah) says they will come to the World to Come, and proves it from the shofar verse. Rabbi Yochanan adds that here Rabbi Akiva set aside his usual habit of finding the good in Israel, as Rashi (the main medieval commentator on the Gemara) explains. He quotes Yirmiyahu 3:12, where God tells the prophet to call out to the north: "Return, faithless Israel. I will not stay angry forever."
So the verse behind this blessing sits in the middle of a real argument, and Rabbi Yehuda HaNasi and Rabbi Yochanan take the hopeful side. The prayer itself does not pick a side or name any tribe. The Sefard wording asks to gather "our exiles," and the Rambam's version of this line says "all our exiles."
Yeshayahu 27:13,Radak on Yeshayahu 27:13,Melachim II 17:6,Mishnah Sanhedrin 10:3,Sanhedrin 110b with Rashi,Rambam, Order of Prayer 2:11What does a good harvest have to do with bringing people home?
This blessing comes right after the blessing for rain and a good year. The Gemara (Megillah 17b) asks why, and answers with a verse from Yechezkel (Ezekiel, a prophet who was himself in exile). He speaks to the mountains of the Land of Israel: "Give your branches and bear your fruit for My people Israel, for their return is near."
Notice who the fruit is for. It is not for the mountains. It is for "My people Israel," and the reason given is that they are about to arrive. The harvest in that verse assumes people are on their way. Yechezkel goes on to describe towns resettled, ruins rebuilt, and people and animals multiplying (Yechezkel 36:10-11).
Rabbi Abba made this a sign. He said there is no clearer sign of the end of exile than this verse (Sanhedrin 98a). Rashi explains: when the Land of Israel gives its fruit generously, the end is near.
Yeshayahu also pictures the gathering as a harvest. In the verse right before the shofar, God beats the crop loose and then "you will be picked up one by one" (Yeshayahu 27:12). Rashi says the beating and the picking up go together, like someone who beats his olives and then gathers them.
The Gemara in Megillah keeps going. Once the exiles are gathered, it says, judgment is carried out on the wicked, and it quotes Yeshayahu 1:25-26, including "I will restore your judges as at first." The next blessing in the Amidah is about judges.
Megillah 17b,Yechezkel 36:8-12,Sanhedrin 98a with Rashi,Yeshayahu 27:12 with Rashi,Yeshayahu 1:26