Joseph discusses Malachi 4 and Elijah and the importance of a welding link/sealing between fathers and children.
"Letter to the Church, 7 September 1842 [D&C 128]," p. 5-6, The Joseph Smith Papers website, accessed September 7, 2021
I will give you a quotation from one of the Prophets which had his eye fixid on the restoration of the priesthood the glories to be revealed in the last days, and in an especial <manner> this most glorious of all subjects belonging to the everlasting gospel viz the baptism for the dead, for Malachi says last Chapter verses 5th & 6. Behold I will send you Elijah the Prophet before the coming of the great and dreadful day of the Lord: and he shall turn the heart of the fathers to the children, and the heart of the children to their fathers, lest I come and smite the earth with a curse”. 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.