Alpha and Omega are the first and last letters of the Greek alphabet. The use of these terms as titles of the Lord Jesus Christ has a dual application.
First, they are used to imply the eternal nature of Jesus as a member of the Godhead, or as the scriptures refer to him, “the Eternal One.” This indicates that “he is an everlasting and eternal being in whom all fulness and perfection dwell” (Bruce R. McConkie, Promised Messiah, p. 167).
Second, the phrase “the beginning and the end” have reference to the Atonement and that Jesus is both the beginning, or author, and the end, or finisher, of the salvation of men (see Hebrews 5:9; Hebrews 12:2; Moroni 6:4).
Elder Bruce R. McConkie observed that Christ is not the “author” of salvation if that means the innovator of the plan of redemption, but rather he is the “cause thereof; that is, salvation is possible because of his atoning sacrifice” and that “he is the ’leader’ in the cause of salvation” (Mormon Doctrine, p. 66).