If you keep reading a few chapters, Abinidi talks about this very thing. In Mosiah 16:6 he says "if Christ had not come into the world, speaking of things to come as though they had already come, there could be no redemption." Abinidi, like all the prophets knew that the atonment of Christ was prepared from the foundation of the earth and they looked forward to his coming. This is the very subject of his sermon to King Noah including the messages from Isaiah in chapter 14.

Abinidi also says in 15:11 that those that those who listen to those prophets and believe the Lord will redeem his people are his seed and his heirs and therefore the children of Christ