JS describes ordinances for the dead as creating a welding link "between the fathers and the children."
Joseph Smith Jr., Letter to the Church, September 7, 1842, The Joseph Smith Papers website, accessed November 8, 2021
I might have rendered a plainer translation to this, but it is sufficiently plain, to suit my purpose as it stands. It is sufficient to know in this case that the earth will be smitten with a curse, unless there is a welding link of some kind or other, between the fathers and the children, upon some subject or other. And behold, what is that subject. It is the baptism for the dead. For we without them cannot be made perfect; neither can they without us be made perfect. Neither can they, or us, be made perfect without those who have died in the gospel also; for it is necessary in the ushering in of the dispensation of the fulness of times; which dispensation is now beginning to usher in that a whole, and compleat, and perfect union, and welding together of dispensations and keys and powers and glories should take place, and be revealed from the days of Adam even to the present time; and not only this, but that those things which never have been revealed from the foundation of the world but have been kept hid from the wise and prudent shall be revealed unto babes and sucklings in this the dispensation of the fulness of times. Now what do we hear in the gospel which we have received? a voice of gladness! a voice of mercy from heaven! & a voice of truth out of the earth, glad tidings for the dead; A voice of gladness for the living and the dead; glad tidings of great joy