Rhetorical: There are three elements in this particular sentence, and each one is a planned and important point in Alma's sermon. Alma needs to establish the important elements of connection between their current situation and that of his father's church by the Waters of Mormon. The first point he makes is that they were in bondage to the Lamanites. While this is certainly historically accurate, it is also a point that Alma wants to make for the current situation. The social ideas of the Nehors follow those of the Lamanites, and were precisely the types of changes that King Noah had made in Lehi-Nephi. Alma purposefully reminds his congregation of the bondage because he wants to highlight that the current contentions (with the order of the Nehors) would lead to a similar bondage.
Alma's second point is that Alma's people were delivered from the bondage of the Lamanites through the power of God. Certainly Alma wanted to highlight to his own people the power of faith in God, and the power of God to deliver from this type of bondage. This sets up the argument that their current situation will also be resolved through the power of God.
Alma's final comment is that his father's people came to the land of Zarahemla and in Zarahemla established churches. Since Alma is currently preaching to a church, this brings the history clearly to the present. Symbolically, this current church will have the same option as that earlier church, and it too may be delivered by the word of God.