When Nephi was approximately 72 years of age, he selected his younger brother Jacob to succeed him in supervising the spiritual affairs of the people of Nephi. Jacob was probably about 18 years younger than Nephi. He was born after Lehi's colony had left Jerusalem. In fact it appears that he must have been born during a period of much tribulation, and as a child he suffered great affliction and much sorrow, it says, from the rudeness of his older brethren.
Nevertheless, Jacob was greatly blessed of the Lord, and while still in his youth he beheld the Savior. He saw the days of his ministry in vision. After arriving in America Lehi instructed Jacob to follow Nephi, and when the colony split up Jacob loyally carried out this instruction to accompany Nephi into the wilderness. Sometime later Jacob was called of God and ordained after the holy order of the priesthood. He was consecrated by Nephi.
Jacob was given an assignment by Nephi to read and explain portions of Isaiah to the people. And in this exposition Jacob revealed a most profound knowledge of scripture and also of prophecy. He could teach the Nephites those things that went clear back to the creation of the world. During his dissertation he revealed that an angel had appeared to him just before his sermon, and gave him more details concerning the ministry of Christ then he had known before And we learn that he also knew many facts concerning America as a result of these visitations. In 544 B.C.when Jacob would have been around 54 years of age, Nephi turned over the small plates of Nephi to him. This was one of the greatest scriptural treasures in existence, and this is where the book of Jacob begins.
We should note in passing that Jacob was instructed to engrave on these plates only those revelations which he felt were great. One almost automatically reacts to this statement by asking, "Are not all revelations of God great?" As a direct communication from heaven we should say yes, but in the economy of heaven the Lord has always felt that his servants should select from the multitude of revelations which come with each new dispensation those instructions which are especially significant on a long-range basis for them. It is a reflection on the Lord's love and confidence in his chosen servants that he allows them to decide which revelations they consider the most important.
The Lord had his servants do this in our day just as Jacob was instructed to do it in selecting the material which would go into the small plates.