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.