These are principles in relation to the dead and the living that cannot be lightly passed over, as pertaining to our salvation. For their salvation is necessary and essential to our salvation, as Paul says concerning the fathers that they without us cannot be made perfect neither can we without our dead be made perfect.
Doctrine and Covenants 128:15
"Revelation comes to individual members as they are led to discover their family records in ways that are miraculous indeed," said Elder Boyd K. Packer of the Quorum of the Twelve, in October 1975 general conference.
"Every Latter-day Saint is responsible for this [vicarious] work. Without this work, the saving ordinances of the gospel would apply to so few who have ever lived that it could not be claimed to be true."