According to Dennis Largey, one strength of the Book of Mormon is that it restores and expands upon doctrinal concepts that are only briefly mentioned in the Bible. One example is found in the New Testament book of Romans. The apostle Paul described himself as the apostle of the Gentiles (Romans 11:13). In his epistle to the Romans he referred to the Gentiles as being a wild olive tree, to be grafted into the natural tree (i.e., Israel), to partake of the root. He told the Gentile audience that the natural branches were broken off because of unbelief and warned them that since "God spared not the natural branches, take heed lest he also spare not thee. . . . For I would not, brethren, that ye should be ignorant of this mystery, lest ye should be wise in your own conceits; that blindness in part is happened to Israel, until the fulness of the Gentiles be come in" (Romans 11:21,25; italics added).
Here, there is no sustained discussion concerning his reference to "the fulness of the Gentiles." By way of commentary, in 1 Nephi 15:7 we read: "And they [Laman and Lemuel] said: Behold, we cannot understand the words which our father hath spoken concerning the natural branches of the olive-tree, and also concerning the Gentiles." In reply, Nephi taught:
Behold, I say unto you, that the house of Israel was compared unto an olive tree, by the Spirit of the Lord which was in our father; and behold are we not broken off from the house of Israel?
And now, the thing which our father meaneth concerning the grafting in of the natural branches through the fulness of the Gentiles, is, that in the latter days, when our seed shall have dwindled in unbelief, yea, for the space of many years, and many generations after the Messiah shall be manifested in body unto the children of men, then shall the fulness of the gospel of the Messiah come unto the Gentiles, and from the Gentiles unto the remnant of our seed. (1 Nephi 15:12-13; italics added)
Here Nephi not only answered his brothers' questions, but also gave the New Testament student a definitive statement of interpretation to Paul's reference. In the latter days, the fulness of the gospel would come to the Gentiles, and the Gentiles would then take it to the house of Israel. This would cure the blindness that "happened to Israel" which Paul talked about in Romans 11, for as Nephi further taught, "They shall be brought out of obscurity and out of darkness; and they shall know that the Lord is the Savior and their Redeemer, the Mighty One of Israel" (1 Nephi 22:12). [Dennis Largey, "The Book of Mormon, an Interpretive Guide to the New Testament," in The New Testament and the Latter-day Saints, 1987, pp. 138-139] [For a much greater elaboration on the concept of the wild olive-tree, see the commentary on Jacob 5--Zenos' Allegory of the Tame and Wild Olive Tree]