Both Lord Wilmore and I have written about the veil before. See here and here. God's presence (heaven) and the material creation (earth) are separated by a veil. Rending the veil opens the pathway for man into God's presence and unites heaven and earth. This is symbolically represented by the temple. There are different ways and occasions where the veil can and will be rent. This became clearer to me as I read D&C 101 recently, which I will get to soon. Here are three ways of rending the veil:
Rending the personal veil of unbelief
And there were many whose faith was so exceedingly strong, even Christ came, who could not be kept from within the , but truly saw with their eyes the things which they had beheld with an eye of faith, and they were glad. (Ether 12:19)
The brother of Jared is one example of rending the veil by seeing with the eye of faith. King Lamoni also has an experience where the veil of unbelief is dispelled.
the dark of was being cast away from his mind, and the which did light up his mind, which was the light of the glory of God (Alma 19:6)
The veil being removed and the light shining, in fact reminds of the veil taken off from the eyes of the Brother of Jared and seeing the finger of God giving light to the stones in Ether 3. The point is that unbelief and pride is withholding a portion of light from us, preventing all of us from seeing clearly.
And if your eye be to my , your whole bodies shall be filled with light, and there shall be no darkness in you; and that body which is filled with light all things. (D&C 88:67)
The glory of God is represented by the holy of holies / celestial room in the temple. If our eye is single to his glory, we are seeing beyond the veil into the light. Even though Christ has prepared a way into the holy of holies as I soon will show, we must each rend our personal veil of unbelief to walk that way.
Christ's first coming: The way to salvation prepared
Christ's second coming: His glory revealed
Christ completed his atoning sacrifice when he come to earth the first time in a mortal tabernacle. He promised to come again in glory. D&C 101 explains that he will rend the veil separating heaven and earth at his second coming. Notice the temple symbolism.
And for the revelation which is to come, when the of the covering of my temple, in my tabernacle, which hideth the earth, shall be taken off, and all flesh shall me together. (D&C 101:23)
There is also an apt reference to Isaiah 40, that I did not pick up until I read the footnote of the verse.
And the of the Lord shall be , and all flesh shall it together (Isaiah 40:5)
According to Bible scholar, Margareth Barker, the setting of Isaiah 40 is the holy of holies. The glory of God was exactly what King Lamoni could see when the veil was cast away from his mind as I just quoted in Alma 19. At the second coming ("the revelation which is to come"), the veil of the temple shall be lifted once more in a way that reveals his glory to the whole earth and all flesh shall see it. Those who are not prepared will be consumed. D&C 101 continues:
24 And every thing, both of man, or of the beasts of the field, or of the fowls of the heavens, or of the fish of the sea, that dwells upon all the face of the earth, shall be ;
25 And also that of element shall with fervent heat; and all things shall become , that my knowledge and may dwell upon all the .
The material creation cannot endure this glory. This is why a veil must separate the two in the first place. But we can prepare to endure the day by rending our personal veil of unbelief and follow Christ into the holy of holies. Then we can dwell on an earth where also his "knowledge and glory" dwells, an earth that is no longer separated from heaven by a veil. The bride removes her veil after she has become married to the groom. When the earth lifts her veil, we have a marriage of heaven and earth.