And now, my dearly beloved brethren and sisters, let me assure you that these are principles in relation to the dead and the living that cannot be lightly passed over, as pertaining to 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. - D&C 128:15
Elder David B. Haight of the Council of the Twelve, in his April 1991 general conference address, commented on why the Church is so committed to ancestral research."Our answer is simple, yet profound: Because we love them. Because they are entitled to the same blessings that we enjoy. Because this is a major part of the heavenly plan for this, the dispensation of the fulness of times, for the blessing of all people."