Together with Isaiah and Jacob, Nephi bore witness to the reality of the Redeemer (see vv. 2–3). The importance of these three witnesses is explained by Daniel H. Ludlow:
“God has said through his prophets, ‘In the mouth of two or three witnesses shall every word be established.’ (2 Corinthians 13:1.) Nephi was apparently aware of this system of witnesses when he introduced three great pre-Christian witnesses of the coming of Jesus Christ: Isaiah, Nephi himself, and Nephi’s brother Jacob. Nephi then continues: ‘Wherefore, by the words of three, God hath said, I will establish my word.’ (2 Nephi 11:3.)”
(A Companion to Your Study of the Book of Mormon, p. 140).
Nephi quoted Isaiah because he delighted in “proving unto my people the truth of the coming of Christ” (2 Nephi 11:4). This provides an important insight into the particular passages Nephi chose to quote. Scholars call such passages “messianic” because they center on the Messiah. Watching for such messianic meanings helps an individual better understand Isaiah.
Nephi taught that the law of Moses and many other things were given by God to typify Christ. The word type has a peculiar scriptural meaning. It means that an object or event carries symbolic significance as well as a literal meaning. Thus, Alma says that the Liahona was a type (shadow or symbol) of how one comes to the true promised land (see Alma 37:38–47). To find out how profoundly symbolic the law of Moses was, see Mosiah 3:14–15, 13:29–31, Alma 25:15–16, 34:14, and Galatians 3:21–24.
Nephi quoted Isaiah for at least three major reasons: Nephi delighted in the words of Isaiah (see 2 Nephi 11:2), the words of Isaiah prove the truthfulness of the coming of Christ (see vv. 4, 6), and Nephi felt that readers “may lift up their hearts and rejoice” (v. 8) because of Isaiah’s words.