In the Doctrine & Covenants, an explanation is given to the verse in Malachi about “turning the hearts of children to the fathers”:
Foreshadowing the great work to be done in the temples of the Lord in the dispensation of the fullness of times, for the redemption of the dead, and the sealing of the children to their parents, lest the whole earth be smitten with a curse and utterly wasted at his coming. (D&C 138:48)
This is the reason for the work for the dead, baptism and sealings, that we do in the Temples. All the descendants of Adam will need to be bound together in family relationships. This brings up a variety of issues:
1. Forcing others to become Mormon
While we do baptize as proxy for all of our deceased relatives, whether or not they accept the baptism is their own choice. It is felt that it is better to do the work with the possibility of their rejecting it than to not do the work and have them remain clamoring for it. There was a time when the zeal for getting everyone baptized included random (and not so random) names from various lists, including places like death camps, but it has been repeatedly stressed that you should only do the work for your family, not strangers. Even for immediate family, it should be recommended to talk to those who are living about it before proceeding. If there are objections, then it may have to wait.
2. Sealings to parents or spouses you cannot accept
I’ve seen people worried that they are going to remain sealed to an abusive parent or spouse in the next life because of the sealings that were done at an earlier time. I am sure this is not the case. The Celestial Kingdom will be a place of ultimate joys, not of fear, hostility, or resentment. No matter what sealings were done, no matter what other ordinances were done, they cannot supersede the desire of the people involved. You will not spend forever with a person you cannot stand to be near.
3. Spiritual orphaning
We know that not everyone will accept the Gospel and desire to be sealed for eternity. This creates a minor problem for the others in the relationship. Since these sealings are necessary, it may be needed from time to time for people to be sealed as children to parents who were not their birth parents. I do not believe this will be done lightly, any more than the decision on your placement in your mortal family was done lightly. This should not be anticipated in mortality without all parties alive and in agreement, as we do not know the feelings of those who have passed on, no matter what documents they may have left behind.
Without a great number of records that do not exist or the personal recollections of those who are already dead, we will only be able to scratch the surface of all of the baptism and sealing work that needs to be done. It is, however, important that we do what we can now. It all needs to be done, or as it says in the scripture, the entirety of this world would be a waste.