Alma travels with his friends to give the good news to the people of Anti-Nephi-Lehi. When they meet they not only pass on the good news, but we hear that Alma relates his conversion story to them. Why does he do this?
Alma can feel a kinship to these people who have undergone such a great transformation. While his own transformation was perhaps not quite the distance that these people had had to come, nevertheless he was pulled from a position of fighting against the church to one of leading it. In that similarity there would have been a great sharing of spirit.