Alma’s sermon to the people of Ammoniah is deeply influenced by his personal history and background.
Time and again, he returns to the themes of bondage and delivery. He hearken a back to the time when his father and his people were bound by the Lamanites and he urged the people to remember their miraculous deliverance.
Alma’s attitude towards the Lamanites is also influenced by his experiences. He sees the Lamanites as blinded rather than overtly wicked. His people saw that King Noah and his priests were far worse than the Lamanites and spurned on the hatred of the Lamanites.
He also sees the potential for the Lamanites to be redeemed because he himself was redeemed. His declaration that “the Lord will be merciful unto all who call on his name” is born in the crucible of his experience. He knows that God redeemed him even though he was a vile sinner, and so feels confident that the Lord can help anyone.
Finally, when Alma speaks of angelic ministration he again speaks from recent experience. He would have known that the same angel that visited him also visited Amulek, and likely others. He would have had firm confidence given his recent experience that the Lord had prepared a way and prepared the hearts of many to hear his words.