Jesus has been speaking of a gathering of Israel that was important information for those in Bountiful, but was nothing that would occur in their lifetimes, nor of any descendants they would ever know. What did it mean for them?
It meant that they were part of God’s plan, and that their current part was much more easily understood: “And whosoever will hearken unto my words and repenteth and is baptized, the same shall be saved. Search the prophets, for many there be that testify of these things.”
Although this admonition to repent and be baptized is the succinct summary of Christ’s gospel, it clearly included more that they should learn to do. Therefore, they were to search the prophets, for the prophets knew of the lessons that the people should learn.