Why do Mormons do family history or genealogy work?

I think all people feel a desire to know where they come from. Knowing this gives you a sense of belonging, a tradition of values and stories, and a culture. In the church, our desire for connection extends beyond this, to a spiritual and eternal connection. We believe that to be truly happy in this life and the next, we need the gospel of Jesus Christ and to make commitments/covenants with with (like baptism). However, so many people have died without knowing about Chris or having the chance to make promises to him. This would be totally unfair if Heavenly Father had not provided another route. In sacred temples, we perform this necessary ordinances for ancestors who have died with knowing or having the chance to accept Christ. We believe that our ancestors will then have the choice to accept this work or not from the next world. Furthermore, because we believe in the eternal nature of the family, we seal our ancestors as family units to us in the holy temple. This way, all of us are eternally a family with God.