The priesthood revealed

The record of this being fulfilled is in Doctrine and Covenants 110 where Christ accepts the dedicated Kirkland temple before Moses commits the keys of his dispensation to Joseph and Oliver—keys for the gathering of Israel—and Elias commits the keys of the dispensation of the gospel of Abraham—which was the covenant through which all the earth would be blessed through the seed of Abraham, ie. the good news of salvation made available through Christ—and Elijah committed the keys of the last dispensation which would turn the hearts of the children to the fathers and, as described in Section 128, provide “a welding link…between the fathers and the children…{through} baptism for the dead.”

The dispensation of the fullness of times is marked by the consolidation of the keys of prior generations which include gathering Israel (the keys of Moses) and then beyond Israel spreading the message of Christ to all the nations of the earth (the keys of Elias unlocked after the ministry of Christ when Peter was instructed to take the gospel among the gentiles), and the keys entrusted to Elijah which are unlocked in this final dispensation to make the covenants of salvation available across generations throughout the history of mankind.

The work of intergenerational vicarious ordinances is the responsibility of this dispensation. It seems likely that baptism for the dead in the dispensation of the early Christian church was confined to the dead of their generation. The work of temples bringing covenants to all generations and not merely the current generation are the unique final ingredient for the salvation of the children of men unlocked in this generation. The church in modern times has a responsibility of greater scope than the church in the meridian of time and to accomplish that greater scope I expect we already have a larger membership now than the church ever did then.