Question: Why is Jesus referred to as both the Father and the Son in the Book of Mormon?
Answer: Jesus Christ is referred to as both the Father and the Son in the Book of Mormon. The Father and the Son are titles, not names. Just think of Joseph Smith Jr.—he was a father and a son, by title.
“And because he dwelleth in flesh, he shall be called the Son of God, and having subjected the flesh to the will of the Father, being the Father and the Son--
“The Father, because he was conceived by the power of God; and the Son, because of the flesh; thus becoming the Father and Son–“ (Mosiah 15:2-3)
Under the counsel and approval of Almighty Elohim, Jehovah became the Father of salvation, the Father of eternal life. Jesus Christ is known as Father by virtue of his role as Creator. Eons before he ever became mortal he was directly involved in creation.
“Behold, I am he who was prepared from the foundation of the world to redeem my people. Behold, I am Jesus Christ. I am the Father and the Son.” (Ether 3:14)
Thus Christ would be both the Father and the Son. He would be called the Father because he was conceived by the power of God, and inherited all of the divine endowments, particularly immortality, from his exalted sire. He would be called the Son because of his flesh—his mortal inheritance from his mother, Mary.
The First Presidency and Quorum of the Twelve explained divine investiture of authority (wherein Christ is given the authority of the Father) as, “In all His dealings with the human family, Jesus the Son has represented, and yet represents Elohim, His Father, in power and authority. . . . Thus the Father placed His name upon the Son; and Jesus Christ spoke and ministered in and through the Father’s name, and so far as power, authority and Godship are concerned, His words and acts were and are those of the Father.”
Source: 400 Questions and Answers About the Book of Mormon by Susan Easton Black,p. 137; Book of Mormon; “The Ministry of the Father and the Son,” in The Book of Mormon: The Keystone Scripture