D&C 124

As the saints began to settle Nauvoo, as He had commanded previously in four other settlements, the Lord said -

"...I command you, all ye my saints, to build a house unto me..." (Doctrine and Covenants Section 124:31)

and also -

"...built unto my name..." (Doctrine and Covenants Section 124:40)

For the purpose -

"...that I may reveal mine ordinances therein unto my people..." (Doctrine and Covenants Section 124:40)

"For therein are the keys of the holy priesthood ordained, that you may receive honor and glory." (Doctrine and Covenants Section 124:34)

For -

"...I will show unto my servant Joseph all things pertaining to this house, and the priesthood thereof..." (Doctrine and Covenants Section 124:42)

"For I deign to reveal unto my church things which have been kept hid from before the foundation of the world, things that pertain to the dispensation of the fulness of times." (Doctrine and Covenants Section 124:41)

Deign meaning -

"to condescend to give or offer" (Merriam-Webster Dictionary)

To reveal hidden things such as -

"...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." (Doctrine and Covenants Section 124:39

The Prophet Joseph Smith explained of the temple -

"What was the object of gathering the Jews, or the people of God in any age of the world? . . .

The main object was to build unto the Lord a house whereby He could reveal unto His people the ordinances of His house and the glories of His kingdom, and teach the people the way of salvation: for there are certain ordinances and principles that, when they are taught and practiced, must be done in a place or house built for that purpose.

It was the design of the councils of heaven before the world was, that the principles and laws of the priesthood should be predicated upon the gathering of the people in every age of the world. Jesus did everything to gather the people, and they would not be gathered, and He therefore poured out curses upon them. Ordinances instituted in the heavens before the foundation of the world, in the priesthood, for the salvation of men, are not to be altered or changed. All must be saved on the same principles.

It is for the same purpose that God gathers together His people in the last days, to build unto the Lord a house to prepare them for the ordinances and endowments, washings and anointings, etc. One of the ordinances of the house of the Lord is baptism for the dead. God decreed before the foundation of the world that that ordinance should be administered in a font prepared for that purpose in the house of the Lord.” (History of the Church, 5:423–24.)