D&C 27

The Lord tells the Prophet that the time would come when -

"...I will drink of the fruit of the vine with you on the earth..." (Doctrine and Covenants Section 27:5)

And then continues that not only him but, Moroni, John the Baptist, Peter, James, and John, Elijah, Joseph, Jacob, Isaac, Abraham, Adam, and others to which keys or blessings of dispensations have been given. And then with them -

"...all those whom my Father hath given me out of the world." (Doctrine and Covenants Section 27:14)

and also -

"...Elias, to whom I have committed the keys of bringing to pass the restoration of all things spoken by the mouth of all the holy prophets since the world began, concerning the last days..." (Doctrine and Covenants Section 27:6)

It seems at first that it would be a individual by the name of Elias that would restore keys of restoration of all things. Why then would you need the others?

There are many references to Elias in scripture and translated scripture including Christ, John the Revelator, and Gabriel. So who is this Elias? Elder Bruce R. McConkie provides an answer to these questions -

“By finding answer to the question, by whom has the restoration been effected, we shall find who Elias is and find there is no problem in harmonizing these apparently contradictory revelations. Who has restored all things? Was it one man? Certainly not. Many angelic ministrants have been sent from the courts of glory to confer keys and powers, to commit their dispensations and glories again to men on earth. At least the following have come: Moroni, John the Baptist, Peter, James, and John, Moses, Elijah, Elias, Gabriel, Raphael, and Michael. (D. & C. 13; 110; 128:19–21.) Since it is apparent that no one messenger has carried the whole burden of the restoration, but rather that each has come with a specific endowment from on high, it becomes clear that Elias is a composite personage. The expression must be understood to be a name and a title for those whose mission it was to commit keys and powers to men in this final dispensation.” (Mormon Doctrine, p. 221; see also D&C 110:12–16.)