There are several uses of this word in the scriptures. (1) It is the New Testament (Greek) form of Elijah (Hebrew), as in Luke 4:25–26, James 5:17, and Matt. 17:1–4. Elias in these instances can only be the ancient prophet Elijah whose ministry is recorded in 1 and 2 Kings. The curious wording of JST Mark 9:3 does not imply that the Elias at the Transfiguration was John the Baptist, but that in addition to Elijah the prophet, John the Baptist was present (see Mark 9:4 note a).
(2) Elias is also a title for one who is a forerunner; for example, John the Baptist, as in JST Matt. 11:13–15, JST Matt. 17:10–14, and JST John 1:20–28 (Appendix). These passages are sufficiently clarified to show that anciently two Eliases were spoken of, one as a preparer and the other a restorer. John was sent to prepare the way for Jesus, Jesus Himself being the Restorer who brought back the gospel and the Melchizedek Priesthood to the Jews in His day (see JST John 1:20–28 [Appendix]). In this particular instance there is reflected also the comparative functions of the Aaronic and Melchizedek Priesthoods.
(3) The title Elias has also been applied to many others for specific missions or restorative functions that they are to fulfill; for example, John the Revelator (D&C 77:14) and Noah or Gabriel (Luke 1:11–20; D&C 27:6–7).
(4) A man called Elias apparently lived in mortality in the days of Abraham, who committed the dispensation of the gospel of Abraham to Joseph Smith and Oliver Cowdery in the Kirtland (Ohio) Temple on April 3, 1836 (D&C 110:12). We have no specific information as to the details of his mortal life or ministry.
Thus the word Elias has many applications and has been placed upon many persons as a title pertaining to both preparatory and restorative functions. It is evident from the questions they asked that both the Jewish leaders and the disciples of Jesus knew something about the doctrine of Elias, but the fragmentary information in our current Bibles is not sufficient to give an adequate understanding of what was involved in use of the term. Only by divine revelation to the Prophet Joseph Smith is this topic brought into focus for us who live in the last days.