Alma continues to speak of the priests of old. These are the teachers, not simply the officiators. The point is that they were to teach the people to know “in what manner to look forward to his Son for redemption.” The essential restored truth of the Nephite gospel is the understanding that the atoning mission of the Messiah is to come, and that it has been part of what prophets and righteous priests taught in the scriptures.
This is the first time in the Book of Mormon that we see an understanding of events of the premortal existence. The priests who preached the true understanding of the mission of the Son were “called and prepared from the foundation of the word according to the foreknowledge of God.” The statement makes it clear that this happened according to God’s foreknowledge, and, therefore, had to occur before the priests were born.
The next thing we learn is that these priests were chosen “on account of their exceeding faith and good works.” Although we might see this as a suggestion that it was their premortal works that qualified them, that probably isn’t the meaning here. Alma notes that they also had to choose between good and evil, and that places the good works in the mortal realm. Thus, the priests have been foreordained, but only upon God’s knowledge of how they will act during their mortal lives. Having them chosen for their works also clearly separates them from the lineage based Levitical priests, who were born into their calling.
This leaves the confusing statement that the righteous and faithful are called with a holy calling which was “prepared with, and according to, a preparatory redemption for such.” The preparatory redemption is the one that prepares us to meet God and stand clean before Him. That is what the Atonement enables. Thus, the priests are called, understanding that they were to preach so that the people might know “in what manner to look forward to his Son for redemption.” The language may be complicated, but the meaning is simply to reiterate what Alma declared in verse 2.