In 1 Nephi 15, Nephi's brothers complain that they cannot understand the meaning of some of their father's words:
7 And they 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.Five chapters earlier, just prior to Nephi's description of his grand vision, we get an account of what Lehi had been teaching his sons. See 1 Nephi 10:12-14:
12 Yea, even my father spake much concerning the Gentiles, and also concerning the house of Israel, that they should be compared like unto an olive tree, whose branches should be broken off and should be scattered upon all the face of the earth.
13 Wherefore, he said it must needs be that we should be led with one accord into the land of promise, unto the fulfilling of the word of the Lord, that we should be scattered upon all the face of the earth.
14 And after the house of Israel should be scattered they should be gathered together again; or, in fine, after the Gentiles had received the fulness of the Gospel, the natural branches of the olive tree, or the remnants of the house of Israel, should be grafted in, or come to the knowledge of the true Messiah, their Lord and their Redeemer.