Verse 21 and the first clause of verse 22 are part of the same concept. The House of Israel is to be established in “this land.” There will be a New Jerusalem and it will be in this land and it will be the place of the ultimate gathering. It will also be the location of the government of the Triumphant Messiah, who is the Savior in his future role. This theme of the New Jerusalem on this land is reiterated in 3 Nephi 21:22-25.
The theme of the New Jerusalem and the gathering is codified in the tenth Article of Faith:
Articles of Faith:10
10 We believe in the literal gathering of Israel and in the restoration of the Ten Tribes; that Zion (the New Jerusalem) will be built upon the American continent; that Christ will reign personally upon the earth; and, that the earth will be renewed and receive its paradisiacal glory.
The understanding of this New Jerusalem as the New World administrative center for the final Government of God comes from what Joseph learned as he translated this discourse of the Savior:
For Latter-day Saints, the gathering of Israel in the last days, and the building of the city of Zion and of the New Jerusalem, are closely related concepts.
“The tenth article of faith, written by the Prophet Joseph Smith in 1842, declares that the New Jerusalem will be built upon the American continent. He learned this as he translated the Book of Mormon (3 Ne. 20:22; Ether 13:2-6). Additional revelation on this subject came in September 1830 and was further clarified in the subsequent months (D&C 28:9; 42:33-36, 62, 67; 57:3). In July 1831, Joseph Smith traveled to Jackson County, Missouri, at the command of the Lord, where it was announced that the long-awaited gathering of Israel would commence. The city of Zion (also called the New Jerusalem) and its temple would be built in Independence, Missouri (D&C 57:1-3).
Even as the ancient tribes of Israel were scattered north of the Holy Land and their identity was lost, their prophets foretold a gathering of Israel in the last days in a consecrated land (Jer. 31:1-12). Zion would be reestablished. This prophecy includes the promise that the “pure in heart” will receive the higher principles and truths of the full gospel of Jesus Christ (D&C 97:21; 100:16; 101:18). Both where and how they live will come about under divine influence. Since favorable spiritual conditions may exist anywhere in the world, cities of Zion and of Zion people, the “pure in heart,” could be located anywhere in the world (D&C 97:21). However, there is to be a “center place,” or capital city, of Zion. It is referred to both as “the city of Zion” and as “the city of New Jerusalem” (D&C 57:2; 84:2; cf. 45:66-67).” (Encyclopedia of Mormonism, 1-4 vols., edited by Daniel H. Ludlow (New York: Macmillan, 1992), 1010.)