Lehi’s teachings were causing “much disputation” among his older sons. Apparently the things he was teaching them were difficult to understand. In particular, the brothers were struggling with the allegory of the olive tree. The olive tree was a symbol that was used by many of the ancient Israelite prophets. This type of tree lent itself particularly well to a description of the House of Israel.
Grafting is a horticultural process of uniting two genetically compatible plants so that they grow as one. This is done by surgically inserting a branch or shoot of one plant into the tissue of another; after the union heals, they are a single living entity. The purpose of grafting is most often to unite a root stock with grafted parts that together produce some desired result. Some varieties of olive trees had very vigorous roots, but produced poor olives, and vice-versa, so branches from good quality olive trees were grafted onto olive trees of stronger root stock which together made an all-round superior olive tree.
The olive tree allegory is explained so much in the Book of Mormon that it is hard for today’s readers to understand why Lehi’s sons had such difficulty with the concept. Here in chapter 15 Nephi gives his brothers some insight into where they fit in the allegory. Lehi’s family is a branch of the House of Israel which has been broken off of the natural olive tree and planted elsewhere (v. 12). In the latter days, the gospel will be given to the Gentiles. Through them, Lehi’s descendants and the rest of the natural branches will receive the fulness of the Gospel of the Messiah and be grafted back in to the true olive tree.
The olive tree allegory helped Lehi’s sons to see their place in the House of Israel. I have a feeling that they were not so pleased that they had been broken off and would not be considered a part of the Lord’s covenant people until many generations had passed away. But after they had reached an understanding of this concept, Nephi was able to teach them the words of Isaiah “who spake concerning the restoration of the Jews, or of the House of Israel; and after they were restored they should no more be confounded, neither should they be scattered again.”
The Book of Mormon claims that the olive tree allegory originates with the prophet Zenos (whose writings are no longer extant). Jacob quotes Zenos’ allegory in full in Jacob 5. Biblical passages seem to cite the allegory as if the reader were already familiar with it. (see esp. Romans 11:16-25) The verses in Romans and Jacob’s treatise are so clearly parallel that they likely share a common source.
Romans is an excellent chapter to read along with 1 Nephi 15. Paul asks in Rom 11:1 “Has God cast away his people? God forbid.” Nephi explained to his brothers that by breaking off the natural branches and bringing Lehi’s family to the Americas, he was scattering them, but not casting them away. They would have an opportunity to be restored into the olive tree in the last days. Romans 11:11 states “I say then, have they stumbled that they should fall? God forbid. But rather through their fall, salvation is come unto the Gentiles.” Here we see that God’s plan was always for the Gentiles to bring the House of Israel to a knowledge of their Redeemer. Finally, verses 26 and 27 sum up the matter: “And so all Israel shall be saved: as it is written, There shall come out of Zion the Deliverer, and shall turn away ungodliness from Jacob: For this is my covenant unto them, when I shall take away their sins.” Nephi concurs: “they shall come to the knowledge of their Redeemer and the very points of his doctrine, that they may know how to come unto him and be saved.”