Journal of Discourses, Brigham Young 13:38

Do you know what the Millennium is for, and what work will have to be done during that period? Suppose the Christian world were now one in heart, faith, sentiment and works, so that the Lord could commence the Millennium in power and glory, do you know what would be done? Would you sit and sing yourselves away to everlasting bliss? No, I reckon not. I think there is a work to be done then which the whole world seems determined we shall not do. What is it? To build temples. We never yet commenced to lay the foundation of a temple but what all hell was in arms against us. That is the difficulty now: we have commenced the foundation of this temple. What are we going to do in these temples? Anything to be done there? Yes, and we will not wait for the Millennium and the fullness of the glory of God on the earth; we will commence, as soon as we have a temple, and work for the salvation of our forefathers; we will get their genealogies as far as we can. By and by, we shall get them perfect. In these temples we will officiate in the ordinances of the Gospel of Jesus Christ for our friends, for no man can enter the kingdom of God without being born of the water and of the Spirit.

Journal of Discourses, John Taylor 24:27

The spirit of rebellion has gone on ever since the devil and his angels were cast out of heaven. He and they have been making war against the Saints, and will continue to do so; but Satan will finally be over come. Before that, however, Satan will be bound for a thousand years, and during that time we will have a chance to build temples and to be baptized for the dead, and to do a work pertaining to the world that has been, as well as to the world that now is, and to operate under the direction of the Almighty in bringing to pass those designs which He contemplated from the foundation of the world.

Journal of Discourses, Wilford Woodruff 19:35

I have felt to rejoice exceedingly in this work of redeeming the dead. I do not wonder at President Young saying he felt moved upon to call upon the Latter-day Saints to hurry up the building of these Temples. He felt the importance of the work; but now he has gone, it rests with us to continue it, and God will bless our labors and we will have joy therein. This is a preparation necessary for the second advent of the Savior; and when we shall have built the Temples now contemplated, we will then begin to see the necessity of building others, for in proportion to the diligence of our labors in this direction, will we comprehend the extent of the work to be done, and the present is only a beginning. When the Savior comes, a thousand years will be devoted to this work of redemption; and Temples will appear all over this land of Joseph–North and South America–and also in Europe and elsewhere; and all the descendants of Shem, Ham, and Japheth who received not the Gospel in the flesh, must be officiated for in the Temples of God, before the Savior can present the kingdom to the Father, saying, “It is finished.”