Alma 8:31

and they had power given unto them, insomuch that they could not be confined in dungeons; neither were it possible that any man could slay them; nevertheless they did not exercise their power until they were bound in bands and cast into prison. Now this was done that the Lord might show forth his power in them.

They were given power. No one could lock them up. No one could kill them. But they did not use their power until they were tied up and thrown in prison. This happened so the Lord could show his power through them.

They were given such power that they couldn’t be confined in prison cells, and no one could kill them. Yet they didn’t use this power until after they were bound in chains and thrown into prison—so the Lord could show his power through them.