Why is the salvation of the dead necessary for my salvation?

And now, my dearly beloved brethren and sisters, let me assure you that these are principles in relation to the dead and the living that cannot be lightly passed over, as pertaining to our salvation. For their salvation is necessary and essential to our salvation, as Paul says concerning the fathers—that they without us cannot be made perfect—neither can we without our dead be made perfect. (D&C 128:15)

I’ve read over this verse a number of times and I have always wondered why Joseph Smith said that the salvation of the dead is necessary for our salvation and why the dead can’t be made perfect without us and we can’t be made perfect without them. I wonder about this because I am used to thinking of salvation as an individual affair subject to the grace of God and the willing agency of each person. I can’t control other people and what they do, so why is it that my salvation hinges upon someone else long dead receiving salvation? And why does their salvation hinge upon me receiving mine? And why and how does our attainment of perfection depend upon each other?

I read over these verses:

17 And again, in connection with this quotation I will give you a quotation from one of the prophets, who had his eye fixed 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, namely, the baptism for the dead; for Malachi says, last chapter, verses 5th and 6th: 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.
18 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 nor we 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 complete 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 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. (D&C 128:17-18)

I found the answer in verse 18:

…for it is necessary…that a whole and complete 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.

This suddenly suggested to me that the work for the dead is about welding together the various gospel dispensations that were separated from each other by the unbelief, apostasy, and ignorance of the various generations of children (or parents) throughout the history of the earth.

And then again, in verse 18 I read it again:

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… For we without them cannot be made perfect; neither can they without us be made perfect.

I realized that it isn’t just the perfection of individuals we are seeking. As Heavenly Father and Heavenly Mother want us to become like them, exalted fatherhood and motherhood is the pinnacle of celestial attainment and perfection. We’re also seeking perfect marriage so that we can have a perfect family (or rather a perfected family). Neither the woman without the man, nor the man without the woman in the Lord.

We know this, yes?

But along with this, you can’t have a perfect family without children. You also can’t have a perfect family without parents. Neither the parents without the children, nor the children without the parents in the Lord. There has to be a welding link between generations, otherwise the earth would suffer the eternal curse of having some without parents and others without children. There must be a complete establishment of the patriarchal order so that those who are worthy to have righteous parents (whose parents may have broken their covenants or refused them) can have the satisfaction of being sealed to righteous and worthy grandparents or other ancestors. And those with wayward children can receive to themselves their worthy grandchildren and great-grandchildren while the wayward children stand as ministering angels. And those who suffered childlessness can receive the spiritually orphaned through adoptive sealing.

Conclusion: The family is of God. The full family.