During His earthly ministry, the Lord Jesus Christ conveyed the gospel first to the Jewish people, from which lineage He descended. He then directed that His Apostles and servants take the gospel to the Gentiles in surrounding lands. In the dispensation of the fulness of times, the order was reversed, the restored gospel going first to the Gentiles, among whom were mingled those of Israelite heritage, and then to the remnant of the house of Israel, including the descendants of the Lamanites and, eventually, to the Jewish people themselves. President Joseph Fielding Smith summarized this principle succinctly:
FIRST TO BE LAST AND LAST TO BE FIRST. In the former dispensation, the gospel was first preached to the Jews and then, after they had rejected it, it was taken to the Gentiles. In the dispensation in which we live, the gospel was first taken to the Gentile nations, and scattered Israel other than the Jews were gathered out; and after being preached among the Gentile nations, it shall go to the Jews, the first being last and the last being first, as the Savior promised. [Compare Matthew 19:30; 20:16.] (Doctrines of Salvation, 3 vols., ed. Bruce R. McConkie [Salt Lake City: Bookcraft, 1954–1956], 3:259)
Jacob is familiar with this principle from his studies of the brass plates and from statements by his brother Nephi. According to the message conveyed to Nephi by an angel of God we learn: “And the time cometh that he shall manifest himself unto all nations, both unto the Jews and also unto the Gentiles; and after he has manifested himself unto the Jews and also unto the Gentiles, then he shall manifest himself unto the Gentiles and also unto the Jews, and the last shall be first, and the first shall be last” (1 Nephi 13:42; compare Ether 13:12; D&C 29:30; 88:59).