JOEL - The requirement of temples as a sign of the true church is mostly based on latter-day revelation. In a revelation to the Prophet Joseph Smith regarding temples, endowments, and sacred ordinances, the Lord explained that these have been associated with the true church in every dispensation:

"Therefore, verily I say unto you, that your anointings, and your washings, and your baptisms for the dead, and your solemn assemblies, and your memorials for your sacrifices by the sons of Levi, and for your oracles in your most holy places wherein you receive conversations, and your statutes and judgments, for the beginning of the revelations and foundation of Zion, and for the glory, honor, and endowment of all her municipals, are ordained by the ordinance of my holy house, which my people are always commanded to build unto my holy name.
And verily I say unto you, let this house be built unto my name, that I may reveal mine ordinances therein unto my people;" (D&C 124:39-40)

Malachi promised that in the last days the Lord would suddenly come to his temple(Mal. 3:1). God is expecting that the children of His true church will have one ready for Him when He comes. Isaiah identified temple building as a sign of the gathering of Israel preparatory to the coming of Christ (Isa. 2:1-3). Other prophetic promises include the building of temples in both the Jerusalem of old and the New Jerusalem of Jackson County (D&C 84:4; D&C 124:36).