King Benjamin’s words on salvation coming only through Christ, paraphrased by Helaman, were given in his last major speech before his death “And moreover, I say unto you, that there shall be no other name given nor any other way nor means whereby salvation can come unto the children of men, only in and through the name of Christ, the Lord Omnipotent” (Mosiah 3:17; see also 4:7–8). Peter quoted the doctrine to Annas, the Jewish high priest, and his kindred in Jerusalem. “Neither is there salvation in any other: for there is none other name under heaven given among men, whereby we must be saved (Acts 4:12). Was Peter also quoting from the Old Testament. Although this is the only reference in the Bible to the doctrine, it is quoted often in the Book of Mormon (see 2 Nephi 9:41; 25:20; 31:21).
The words of Amulek to Zeezrom regarding the impossibility of saving people “in their sins” (Helaman 5:10) are again quoted but slightly different by Helaman than by Amulek as recorded in Alma 11:34. In that incident, Zeezrom asks Amulek the question and Amulek answers in the negative, and refers to the word of God. Helaman’s explanation to his sons expounds on why Amulek answered in the negative (v. 11). Zeezrom really knew better than his question implied, therefore, Amulek probably didn’t need the explanation that Helaman gave his sons.
The building upon the rock of Christ admonished by Helaman (v. 12) is also a New Testament concept that is not found in our present Old Testament. The Sermon on the Mount (Matthew 5:7) concludes with a comparison of the wise man building upon the rock and the foolish man building upon a sandy foundation (see Matthew 7:24–27). The nearly identical sermon given by Jesus to the Nephites in Bountiful in A.D. 34 is prefaced with an admonition to build upon the rock of Christ so that the gates of hell will not prevail against it.
39 Verily, verily, I say unto you, that this is my doctrine, and whoso buildeth upon this buildeth upon my rock, and the gates of hell shall not prevail against them.
40 And whoso shall declare more or less than this, and establish it for my doctrine, the same cometh of evil, and is not built upon my rock; but he buildeth upon a sandy foundation, and the gates of hell stand open to receive such when the floods come and the winds beat upon them. [3 Nephi 11:39–40]
It seems probable that the Matthew account may have had a similar preface, which has been lost. The book of Helaman is a witness for the views that building upon the rock of Christ was once an Old Testament teaching, and also that the prevailing of the gates of hell may have been a part of the Old Testament teaching as well.
The many other things that were taught by Helaman to his sons (Helaman 5:13) may also add to our knowledge of parts lost from the Old Testament.