The introduction of Samuel the Lamanite comes directly after the statement that the Lamanites are faithful. This is an essential backdrop to Samuel. In previous times it would be unthinkable that a Lamanite would preach the gospel. However, the righteousness of the Lamanites is so much greater than that of the Nephites that Samuel comes to the Nephites to preach. The reversal is complete. Rather than sending missionaries to the Lamanites, the Lamanites have sent a missionary to the Nephites.
When Samuel comes, it is not surprising that he is rejected. The Nephites have Nephi in their midst, and Nephi has performed two miracles that had only a temporary effect on Nephite repentance. If they were able to harden their hearts after all that Nephi showed them, how much less would they listen to Samuel. As a Lamanite, the Nephites were predisposed to dismiss him.