Christ is both Father and Son in different contexts. Paul taught of the mystery of godliness. Knowing the details now is not God's promise, but believing in "God, the Eternal Father, and in His Son, Jesus Christ, and in the Holy Ghost" is absolutely necessary to receive eternal blessings.
The Book of Mormon clearly differentiates Jesus Christ as the Son of an Eternal Father. He is called the Son (see 2 Nephi 31:18), the Beloved Son (see 2 Nephi 31:11), the Son of God (see 1 Nephi 10:17), the Holy Child (see Moroni 8:3), the Son of the most high God (see 1 Nephi 11:6), the Son of the living God (see Mormon 5:14), Son of our great God (see Alma 24:13), Son of the everlasting God (see 1 Nephi 11:32), Son of the Eternal Father (see 1 Nephi 11:21; 13:40), the Only Begotten of the Father (see Alma 5:48), the Only Begotten Son (see Jacob 4:5, 11; Alma 12:33), Christ the Son (see Alma 11:44), and the Son of Righteousness (see 3 Nephi 25:2).
Having been endowed by Elohim with infinite power, glory, and authority, Jehovah is also “Father.” He is God who spoke and still speaks to the prophets, who designed and reveals laws for the blessing of his people, and who directs the affairs of mortals on earth. We know also that Jehovah is the same being who later came into the world as Jesus Christ. He became a being of dual nature. The Father [that is, Elohim] has never dealt with man directly and personally since the Fall, and he has never appeared except to introduce and bear record of the Son.
Joseph Fielding Smith explained: "The Father has honored Christ by placing his name upon him, so that he can minister in and through that name as though he were the Father; and thus, so far as power and authority were concerned, his words and acts become and are those of the Father."
The phrase “Son of God” alone is used fifty-one times throughout the Book of Mormon text, with variations of this phrase occurring several more times. The phrase “Only Begotten Son” is used five times, “Only Begotten of the Father” four times, and “Son of the living God” four times.
The Savior told the Nephites several times that He and the Father are one—not in personage or physical form, but in purpose. But even more than that, says the Savior, “I am in the Father, and the Father in me, and the Father and I are one” (3 Nephi 11:27; emphasis added; see also 3 Nephi 9:15; 19:23; and 28:10). In other words, the Father and the Son, whether the Son is acting as Jehovah or Christ, are so unified in mind and will that what one thinks, says, and does, the other one thinks, says, and does exactly.
The promise is extended to obedient Latter-day Saints: “The Father and I are one. I am in the Father and the Father in me; and inasmuch as ye have received me, ye are in me and I in you” (D&C 50:43; see also D&C 35:2).