How can we say that the vicarious work done in the temple does any good? Why can my deeds affect souls in the spirit world? I don’t see any connection. I don’t even know what is going on there, so how can I say that what I’m doing is really making any difference?
How would you answer this?
Here’s my best answer. (Caveat: This is doctrine according to Michaela and in no way official church doctrine!)
We are familiar with the principle of Christ's vicarious work for us. Christ suffered for all of our sins so that we won’t suffer for them if we repent (D&C 19:16-17). Christ’s power and authority over life and death makes His vicarious act of sacrifice for us possible.
The next principle it is necessary to understand is expressed by Jesus’s promise to Peter:
18 And I say also unto thee, That thou art Peter, and upon this rock I will build my church; and the gates of hell shall not prevail against it.Those with the keys of the kingdom can perform ordinances that remain in force past death. This is the basis for the sealing of husband and wife and children together. The marriage will last past death. All other ordinances have this similar promise of enduring beyond death.
19 And I will give unto thee the keys of the kingdom of heaven: and whatsoever thou shalt bind on earth shall be bound in heaven: and whatsoever thou shalt loose on earth shall be loosed in heaven. (Matthew 16:18-19, emphasis added)
Because the ordinances performed by those with keys of the kingdom are binding both on earth and in heaven, that implies authority to reach past the gates of hell to pull people out of spirit prison by doing vicarious ordinances on their behalf. Members who have participated in those ordinances for themselves gain the authority to act in place of others who are dead. (Even a twelve-year-old who is baptized and worthy can be baptized for someone else who is dead.)
If saving ordinances could only be done for the living, then that would mean the church doesn’t really have the keys of the kingdom. It would mean that the gates of hell could prevail against the church.
The keys have to be effective both in heaven and on earth, both during mortality and after, to be the keys of the kingdom of God. The kingdom of God is on earth and in heaven. It has power over the devil, and thus over hell. These are God's keys, with God's power.
From the perspective of the world, it is the ultimate cheekiness to claim one has power to release a spirit from hell. There is no way to verify that claim other than to die and find out. This is why revelation and testimony is needed. Even the possibility of such power had to be revealed from on high. The power had to be given from on high. (And it was! Hooray!!) But to have full faith in it, we also need to gain our own testimony of it from the same source. We need to have assurance that our vicarious works are really working and not just some fable made up.
Acting on behalf of those souls we can’t see and have never even met takes real faith, but I believe that was the same type of faith Jesus exhibited when He took upon Himself our sins. I think our demonstrating that kind of faith is part of what makes us “saviors on Mount Zion.”