Elder Jeffrey R. Holland of the Quorum of the Twelve Apostles wrote of the significance of the testimonies of these three great prophets:
“The Lord’s manner of teaching and affirming, especially when it involves a covenant, has always provided more than one testimony. His admonition has always been that ‘in the mouth of two or three witnesses shall every word be established.’ Indeed, when the Book of Mormon was to come forth through the inspired hand of the Prophet Joseph Smith, it was prophesied that ‘three shall … be shown [the plates] by the power of God. … And in the mouth of three witnesses shall these things be established. …
“Those three witnesses were to be Oliver Cowdery, David Whitmer, and Martin Harris. …
“In keeping with this same covenantal principle, it is interesting to note that there were three earlier witnesses—special witnesses—not only of the divine origins of the Book of Mormon but also of Divinity himself. These early witnesses were Nephi, Jacob, and Isaiah, and it is not by coincidence that their testimonies appear so conspicuously at the beginning of this ancient record. …
“… What is known is that most of the ‘greater views’ of the gospel found in the teachings of the small plates of Nephi come from the personal declarations of these three great prophetic witnesses of the premortal Jesus Christ—Nephi, Jacob, and Isaiah. These three doctrinal and visionary voices make clear at the very outset of the Book of Mormon why it is ‘another testament of Jesus Christ.’ …
“One could argue convincingly that the primary purpose for recording, preserving, and then translating the small plates of Nephi was to bring forth to the dispensation of the fulness of times the testimony of these three witnesses. Their writings constitute a full 135 of the [143] pages from the small plates. By the time one has read Nephi, Jacob, and Isaiah in these first pages, a strong foundation has been laid for what Nephi called ‘the doctrine of Christ’” (Christ and the New Covenant [1997], 33–35).