Those deceased persons for whom we perform temple ordinances will rejoice with us as we faithfully perform this sacred vicarious work in their behalf.
Doctrine and Covenants 138:48
48 . . . [G]reat work [is] to be done in the temples of the Lord in the dispensation of the fulness of times, for the redemption of the dead . . .
President Thomas S. Monson said:
“Millions of ordinances are performed in the temples each year in behalf of our deceased loved ones. May we continue to be faithful in performing such ordinances for those who are unable to do so for themselves. I love the words of President Joseph F. Smith as he spoke of temple service and of the spirit world beyond mortality. Said he, ‘Through our efforts in their behalf their chains of bondage will fall from them, and the darkness surrounding them will clear away, that light may shine upon them and they shall hear in the spirit world of the work that has been done for them by their [people] here, and will rejoice with you in your performance of these duties’ [in Conference Report, Oct. 1916, 6].”
(“Welcome to Conference,” Ensign or Liahona, Nov. 2009, 4–5.)