One of the ordinances performed in Mormon temples is baptism for the dead. Mormons believe that through God’s plan, every person who ever has lived, is living, or will live on the earth will have a fair and equal chance to hear about the gospel of Jesus Christ.
This belief is unique among Christians. Many Christians believe that if someone does not have the opportunity to accept Jesus in this life, then that person will be damned in eternity. However, would it be fair to condemn someone who never even heard about Jesus, let alone His gospel? Of course not!
Because God is just and merciful, He prepared a way so that each one of His children can accept the gospel. For many, that opportunity will come in this life; for some, however, that opportunity will come in a place which Mormons call the “spirit world.” This is where we believe that people wait for the judgment and resurrection after they die.
Is there Biblical support for this belief?
Yes, consider Paul mentioning baptism for the dead in 1 Corinthians 15, verse 29. Teaching about the Resurrection, Paul says:
Else what shall they do which are baptized for the dead, if the dead rise not at all? why are they then baptized for the dead?
This doctrine has been reaffirmed through revelation to modern-day prophets.
Does the baptism force people to become Mormon in the next life?
Of course not. One of the central tenets of God’s plan is free agency, or the ability to choose for ourselves. Just as we are free to choose in this life, so are we in the next life. We believe that while people wait in the spirit world, they are taught about the gospel of Jesus Christ. If they accept the gospel, then they will want to receive the necessary ordinance of baptism (see John 3:5). If they do not accept the gospel, then the baptism on their behalf is of no effect.
How does the baptism happen?
There are baptismal fonts in LDS temples. In these fonts, a man who holds the priesthood will baptize someone else “for and in behalf of” the deceased person. In other words, we are baptized by proxy for the deceased individuals.
The doctrine and ordinance of baptism for the dead is a testament to the love that God has for each of His children.