Why are God and Jesus Christ both considered “our Father”?
The concept that Jesus may be called both the Father and the Son is amply explained in the Book of Mormon,
AND now Abinadi said unto them: I would that ye should understand that God himself shall come down among the children of men, and shall redeem his people.
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–
And they are one God, yea, the very Eternal Father of heaven and of earth. (Mosiah 15:1-4)
And now, because of the covenant which ye have made ye shall be called the children of Christ, his sons, and his daughters; for behold, this day he hath spiritually begotten you; for ye say that your hearts are changed through faith on his name; therefore, ye are born of him and have become his sons and his daughters. (Mosiah 5:7)