Doctrine and Covenants 128:12
Herein is glory and honor, and immortality and eternal life--The ordinance of baptism by water, to be immersed therein in order to answer to the likeness of the dead, that one principle might accord with the other; to be immersed in the water and come forth out of the water is in the likeness of the resurrection of the dead in coming forth out of their graves; hence, this ordinance was instituted to form a relationship with the ordinance of baptism for the dead, being in likeness of the dead.
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Herein is glory and honor, and immortality and eternal life--The ordinance of baptism by water, to be immersed therein in order to answer to the likeness of the dead, that one principle might accord with the other; to be immersed in the water and come forth out of the water is in the likeness of the resurrection of the dead in coming forth out of their graves; hence, this ordinance was instituted to form a relationship with the ordinance of baptism for the dead, being in likeness of the dead.