He is the Father as Creator. Christ is referred to in many scriptural passages as “the very Eternal Father of heaven and of earth” (see Mosiah 15:4, 16:15, Alma 11:38–39, Ether 4:7).
He is the Father of all who accept his atoning sacrifice and covenant with him to obey his everlasting gospel. There are numerous scriptural passages that express this relationship (see Mosiah 5:7, 15:10–13, Ether 3:14, D&C 25:1, 34:1–3, 39:1–4).
He is the Father by divine investiture of authority. This means that the Savior is the fully authorized and commissioned representative of his Father, and as such can speak and act for the Father.
The First Presidency and Council of the Twelve explained divine investiture of authority as follows:
“In all His dealings with the human family Jesus the Son has represented and yet represents Elohim His Father in power and authority. This is true of Christ in His preexistent, antemortal, or unembodied state, in the which He was known as Jehovah; also during His embodiment in the flesh; and during His labors as a disembodied spirit in the realm of the dead… . 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”
(in James E. Talmage, The Articles of Faith, p. 471; the entire statement, “The Father and the Son: A Doctrinal Exposition by the First Presidency and the Twelve,” is found on pages 466–73 of The Articles of Faith