Every person who embraces the gospel becomes of the house of Israel. In other words, they become members of the chosen lineage, or Abraham’s children through Isaac and Jacob unto whom the promises were made. The great majority of those who become members of the Church are literal descendants of Abraham through Ephraim, son of Joseph. Those who are not literal descendants of Abraham and Israel must become such, and when they are baptized and confirmed they are grafted into the tree and are entitled to all the rights and privileges as heirs.
(Joseph Fielding Smith, Doctrines of Salvation, 3:245-46)