These verses from the writings of Isaiah are quoted four times in the Book of Mormon. Watchmen are those who publish the good tidings—the gospel of Jesus Christ. They are the prophets and all servants of the Lord who are called to teach, testify, and bring people to Christ.
Two Jerusalems are spoken of: the first is the famous Old Jerusalem in the Holy Land and the second is the New Jerusalem, also called Zion. New Jerusalem, or Zion, will be built in Independence, Jackson County, Missouri. Joseph Smith wrote:
“I received, by a heavenly vision, a commandment in June [1831], to take my journey to the western boundaries of the State of Missouri, and there designate the very spot which was to be the central place for the commencement of the gathering together of those who embrace the fullness of the everlasting Gospel. Accordingly I undertook the journey, with certain ones of my brethren, and after a long and tedious journey, suffering many privations and hardships, arrived in Jackson County, Missouri, and after viewing the country, seeking diligently at the hand of God, He manifested Himself unto us, and designated, to me and others, the very spot upon which he designed to commence the work of the gathering, and the upbuilding of an ‘holy city,’ which should be called Zion—Zion, because it is a place of righteousness, and all who build thereon are to worship the true and living God, and all believe in one doctrine, even the doctrine of our Lord and Savior Jesus Christ. ‘Thy watchmen shall lift up the voice; with the voice together shall they sing: for they shall see eye to eye, when the Lord shall bring again Zion’ [Isaiah 52:8].”58
The words of the song that will be sung have been revealed (D&C 84:99–102). On the Lord’s coming to the New Jerusalem and all the earth seeing his salvation, see Doctrine and Covenants 133:2–5.