Samuel recaps the story of his ministry. He is called to this mission by an angel from the Lord, something that the Nephites ought to believe and respect. The message was one of repentance, but the people rejected him. Note that Samuel understands that some of their rejection had to do with Samuel’s Lamanite heritage. These Nephites were not able to conceive or accept one who might be righteous who was not from their own ranks. Their own prejudices against the Lamanites blinded them to the potential benefits of accepting a Lamanite prophet.
The rest of the reason for rejection was that Samuel taught hard things. He accused them directly. “Because it was hard against [them]” the Nephites reacted angrily. They were not in a spiritually humble frame of mind where the Lord could influence them to accept truth when they heard it.