The missionaries taught “the records and prophecies”—certainly the records of the Nephite gospel and probably the brass plates as well. Although the Nephite defectors among the Lamanites apparently had copies of the brass plates, the Lamanites apparently did not. This makes sense since Nephi took those records when the brothers split into two groups.
Presumably many of the Lamanites may have shared the same unreasoning hatred for the Nephites as Lamoni’s father did (Alma 20:13). Still, many were prepared for Yahweh’s message and accepted it joyfully.