In response to a question about re-baptism and power to perform the ordinance, I would add the following:
Alma was one of the priests of King Noah. In hindsight he knew what he did among them was wicked. (Mosiah 23: 9.) It was in the position as a priest in King Noah's court that Alma received his priesthood authority. (Mosiah 11: 5.) Unlike his peers, Alma was converted by the message of Abinadi, and was moved to repentance. (Mosiah 17: 1-2.) When he repented, he received from God authority to proceed in using his priesthood. (Mosiah 18: 18.) The moment Alma's authority was conferred came after he repented, preached righteousness, asked if others were willing to receive baptism, and proceeded to perform the ordinance. It was at that moment Alma received power through the Spirit. (Mosiah 18: 10-14.)