The Holy Bible, Ephesians 1:10

10 That in the dispensation of the fulness of times he might gather together in one all things in Christ, both which are in heaven, and which are on earth; even in him:

The Doctrine and Covenants, Section 27:13

13 Unto whom I have committed the keys of my kingdom, and a dispensation of the gospel for the last times; and for the fulness of times, in the which I will gather together in one all things, both which are in heaven, and which are on earth;

Journal of Discourses, Orson Pratt 18:7

Before these terrible judgments are sent forth upon the nations of the earth, God will save all who receive the everlasting Gospel by gathering them to one place, where they can serve him and keep his commandments. He will not merely give them some idea, by reading the Scriptures, that he desires them to gather, but John says there will be a great voice from heaven proclaiming–”Come out of her, my people, that ye be not partakers of her sins, and that ye receive not of her plagues.” Then there is to be a gathering of the people of God in the latter days? Yes. Do you marvel to see this people coming forth from all the various nations, leaving the homes of their ancestry, the graves of their ancient fathers, leaving their acquaintances and friends, and gathering up here into these mountain vales? Do you see it? Do you marvel at it? Remember, O ye inhabitants of the earth, who are looking upon these things, that you are beholding the fulfillment of prophecy, prophecy spoken by the Apostle Paul, in the first chapter of his epistle to the Ephesians. Paul saw the gathering; he saw that it would be a new dispensation, a dispensation to come after his day. Let me repeat Paul’s words–”That in the dispensation of the fullness of times he might gather together in one all things in Christ, both which are in heaven, and which are on earth.” Thus you see that all things in Christ are to be gathered together in one. What does this include? Are the inhabitants of heaven to be made one with the inhabitants of the earth that are in Christ? Yes. The dispensation of the fullness of times is to bring about one of the grandest events that our earth has ever experienced–the union of all things in Christ, both in heaven and upon earth. Are the Saints in Christ? As many of you as have been baptized into Christ have put on Christ, consequently if you are in Christ, if you live in the dispensation of the fullness of times, you will be required to take part in this great and grand gathering together of those who are on the earth. But how about all things in Christ in heaven, are they to come too? That is what I have been explaining. When Christ comes the inhabitants of heaven will come with him. The spirits of the righteous of all dispensations, who have not already received a resurrection, will then come forth, and when the trump of the archangel shall sound, the dead in Christ shall rise first. Then those spirits which appear in the heavens will take possession of their renewed immortal bodies which will spring forth from the tomb, and they will be with those who are gathered here on the earth. Then the dispensation will be complete–all things in Christ, whether in heaven or on earth, will be gathered in one.