Because Jehovah-Christ will have a physical body and dwell in the flesh-like every other mortal son and daughter of God -he will be known as the Son of God. At the same time, because he will be conceived by the power of God, and will thus have within him the powers of the Spirit, he will be known as the Father.
In a modern revelation given to Joseph Smith, the Savior explained that He is “the Father because he [Elohim] gave me of his fulness, and the Son because I was in the world and made flesh my tabernacle, and dwelt among the sons of men.” Christ was known as the Son of God because his growth and development-like all the children of God-was gradual, took place line upon line and precept upon precept. That is, he received “grace for grace” and “continued from grace to grace” until he received in the resurrection a fulness of the glory of the Father. “And thus he was called the Son of God, because he received not a fulness at the first.” (D&C 93:4, 12-14; cf. Lectures on Faith 5:2.)