In the Bible, Joseph, son of Rachel and Jacob obtained the birthright in Israel because he was worthy and because it was his natural right. The Book of Mormon, which is a record of the descendants of Joseph has illustrated the importance of the coming of Jesus Christ.

Ezekiel 37:19
"Say unto them,Thus saith the Lord God; Behold, I will take the stick of Joseph, which is in the hand of Ephraim, and the tribes of Israel his fellows, and will put them with him, even with the stick of Judah and will make them one stick, and they shall be one in mine hand."

The scripture is talking about the Book of Mormon as the "stick of Joseph" and the Bible as the "stick of Judah". As Latter-Day-Saints we believe both the Bible and the Book of Mormon to be the word of God. The Book of Mormon testifies of Jesus Christ.

President Monson said:

"I maintain that a strong testimony of our Savior and of His gospel will help see you through to safety. If you have not read the Book of Mormon, read it. If you do so prayerfully and with a sincere desire to know the truth, the Holy Ghost will manifest its truth to you. If it is true - and it is - then Joseph Smith was a prophet who saw God the Father and His son Jesus Christ. The church is true."