Alma has discussed the transformational event. Now he discusses the aftermath. The experience change him is such a way that the entire nature of his mission in life was radically redirected. As much as he had persecuted the church before, after the event he worked to build it. Here is declares that he has been able to feel joy in the success of that new endeavor (see the comments following 2 Nephi 2:25 for a discussion on the nature of joy in the Book of Mormon).