Jesus declared:
Verily I say unto you, yea, and all the prophets from Samuel and those that follow after, as many as have spoken, have testified of me. And behold, ye are the children of the prophets; and ye are of the house of Israel; and ye are of the covenant which the Father made with your fathers, saying unto Abraham: And in thy seed shall all the kindreds of the earth be blessed. The Father having raised me up unto you first, and sent me to bless you in turning away every one of you from his iniquities; and this because ye are the children of the covenant--And after that ye were blessed then fulfilleth the Father the covenant which he made with Abraham, saying: In thy seed shall all the kindreds of the earth be blessed . . . (3 Nephi 24-27)
According to Richard Anthony, after the patriarch Jacob's arrival in the promised land, Rachel gave birth to Jacob's 12th son, and died in the process. Here the story line in Genesis turns to Joseph. Thirteen of the 50 chapters of Genesis are devoted to Joseph. . . . Not only are that many chapters devoted to Joseph, but the prophet Joseph Smith added much to these chapters in the JST (Joseph Smith Translation) specifically about Joseph.
Joseph was designated as the firstborn, or the birthright son. The life of Joseph is more than a fascinating story of a young man sold by his brothers, who rose to prominence in a foreign land, and then saved his family. Joseph's life was a type or shadow of the future of the whole house of Israel from "generation to generation." His life, and episodes in his life are mentioned over and over in the scriptures--particularly in the Old Testament and the Book of Mormon. He and his descendants were types of Christ and types of the father-firstborn relationship until the great winding-up scene.
Joseph's life and what he did for his eleven brothers is a mirror of what Joseph's descendants would do for the tribes of Israel until the end of the world. Joseph is the greatest example of the firstborn concept of which we have record.
Although the Savior did not come directly through his loins, the keys of the priesthood to bring Israel and the gentiles to Christ were centered in Joseph and his posterity through Ephraim and Manasseh. If we understand the life of Joseph, his prophecies and the prophecies about him, particularly the ones by Jacob as recorded in Genesis 50 of the JST, we can begin to understand the Old Testament prophets, who wrote about Joseph and his calling. Isaiah was a particular prophet who seems to have been able to put all of the prophecies about Joseph and his responsibility into "one." [Richard D. Anthony, Isaiah and Joseph,, pp. 37-38, unpublished]