Rhetorical: Alma now hits home this connection between current church and the church of his father. Alma directly asks his people of they remember the captivity of their fathers. While this might seem to indicate a lineal connection to those people, we need not read it as a literal lineage, but rather a spiritual connection to that earlier church.
Alma also moves away from the communal and into the personal in this verse. Where he begins by addressing the entire community and suggests that they should have a communal memory, he makes it much more personal when he suggests that God has already performed a miracle of deliverance for their own souls, and that they should also remember that. He has deftly moved from the group to the individual, from history to the present, and the particulars of each person's conversion and baptism. Even though they might have been Nephites from birth, the establishment of the church apparently required some initiative to join, as there were others of Zarahemla who did not belong to the church.