Context for Zenock: Alma emphasizes that there is a second prophet who has testified of these things, and then adds information about Zenock. Zenock was stoned to death, apparently right after, and on account of, the sermon from which Alma extracted this passage. This tells us more of the world in which Zenock preached. We have noted that the more common understanding of Son of God did not related specifically to the Atoning Messiah, although Zenock is certainly describing the Atoning Messiah.
There are two important pieces of the Old World context here, the first is the anger of God, and the second is the stoning. Both of those aspects tell us that the larger number of people to whom Zenock preached did not have a belief that allowed for the particular interpretation that Zenock is giving. The anger of the Lord tells us that the people were unbelievers, and the stoning tells us that the people thought Zenock to be a blasphemer. It is interesting in this context to note that Zenos was also slain for his testimony (Helaman 8:19). This was not a popular doctrine in the Northern kingdom.
This picture of a people who did not understand the role of the Atoning Messiah in the Old World fits our understanding of the historical situation there, and explains that perhaps both Zenos and Zenock were reforming prophets, who were attempting to bring the correct understanding of the Atoning Messiah to a people who were not willing to accept it. This historical situation makes it a little easier to understand the rather complete Nephite understanding of the Atoning Messiah. This was not a new revelation to the world. The Lord had attempted to offer such an understanding to ancient Israel through Zenos and Zenock (and imagery in other prophets, as Alma will point out next) but that information was rejected, and Zenock was stoned and Zenos was slain.
In the New World, however, we have the beginnings of a people whose very foundation was built upon direct revelation and dramatic spiritual transformation of not only their hearts, but of their culture and place. The early Nephites were in a unique position to accept this teaching, and to embrace it, as they did, and of which they have left us such great testimony.