One of the significant acts of religious law and family life recorded in the Old Testament is that of the bestowal of the birthright blessing.
The Encyclopedia of Mormonism explains: "From Adam to Jacob, the main office of God's priesthood was that of patriarch. Adam, Enoch, Noah, and Abraham administered the Lord's work, established covenants between God and the faithful, recorded their teachings and prophecies, and gave special priesthood blessings. A patriarch could bless his offspring by calling upon the powers of heaven. As he gave the birthright blessing to one of his sons, for instance, the keys and powers of the priesthood were extended to the next generation. In the patriarchal order, under the law of primogeniture, these priesthood rights normally were to be given to the eldest son; from Abraham to Ephraim the birthright blessing went to younger sons because of their righteousness. (Gen. 21, 27-28, 48-49.)"One example of a younger son receiving the blessing rather than the firstborn is the story of Jacob and Esau, twin sons of Isaac and Rebekah. Esau, who was born before Jacob, under the law of primogeniture, was heir to the blessing. However, Esau sold his birthright to Jacob "for bread and pottage of lentiles. . . . " (See Genesis, chapter 25.)
In The Way to Perfection, Joseph Fielding Smith wrote: "We may not know all the circumstances concerning the call of Jacob over Esau, and just why the Lord chose the younger to inherit the rights of Priesthood and appointed the older to serve the younger. We may say in truth that Jacob was more faithful and gave better heed to the commandments of the Lord. This would entitle him to the blessings, for let it be remembered that all blessings are predicated on faithfulness, and this according to a law `irrevocably decreed in heaven before the foundation of the world, . . . and when we obtain any blessing from God, it is by obedience to that law upon which it is predicated.'
D&C 130:20.T On this ground, then, Jacob was entitled to supplant Esau, if there was any such thing as a supplanting. Our history of those events informs us that Jacob was called before he was born to inherit these blessings. Then they were given him by the highest Authority, and who dare question the right of that Authority to bestow the blessings?"