This passage is significant for two reasons. It refers to Christ’s role as merciful mediator. Stephen R. Robinson said:
“Some in the modern Church just seem to have a difficult time acknowledging God’s great mercy to his Saints. This has been a failing in other dispensations as well. For example, Alma quotes the ancient Prophet Zenock to his own people (and to us) as follows: ’Thou art angry, O Lord, with this people, because they will not understand thy mercies which thou hast bestowed upon them because of thy Son’ (Alma 3:16). I believe it is a sin of ingratitude to resist the mercies that have been bestowed upon us because of the Son.” (Following Christ, p. 87)
Secondly, this passage explains, in an Old Testament context, that Christ was to be the Son of God.
Bruce R. McConkie
"Statements by the seers of Old Testament times, which have been preserved for us, that God should have a Son are few and far between… Actually the Book of Mormon tells us more about the usage of the name the Son of God by Old Testament prophets than does that volume of Holy Writ itself. Nephi the son of Helaman, as he sought diligently to prepare his people for the coming of their Messiah, told them that both Moses and Abraham bore record ‘that the Son of God should come’; that ‘many before the days of Abraham’ so certified; that ‘all the holy prophets’ from Abraham to Moses did likewise; and that ’since the days of Abraham there have been many prophets that have testified of these things,’ including Zenos, Zenock, Ezias, Isaiah, and Jeremiah, all of whom labored among Old Testament peoples. The same witness, he said, had been born by ‘almost all of our fathers’ among the Nephites. (Hel. 8:13-23.)
“Alma, with the brass plates of Laban as his source, quoted these words from a prayer of Zenos: (quotes Alma 33:3-16). Fragmentary as our records are, it is nonetheless clear that all of the prophets of Old Testament times knew and taught that the promised Messiah would be the Son of God.” (The Promised Messiah, p. 144)