Chapter 4 was a quotation from Alma the younger’s personal record. Other than the introduction, Mormon simply copied what was in the journal. Mormon closed that chapter when he finished copying. Now he needs to finish the basic story and move to the next event. It is typical of Mormon’s editing to finish a quotation, and then finish the story at the beginning of the next chapter, rather than finish in the same chapter.
Verse 4 simply says that they “began to establish the order of the church in the city of Zarahemla.” That is an interesting conclusion because all of the elements that Mormon indicated, that led to that statement, had already been established prior to the time Alma spoke to the congregation in Zarahemla. The difference was not in the organization, but in the separation of those who would repent and follow Jehovah’s laws and those who would not.
The governing aspects of the church didn’t change, but there was a change in the people, and some of those people did repent. The generic nature of the response suggests that perhaps Alma didn’t say anything specific in his personal record, nor in the official record. Mormon may have given such a generic summation based on his assumptions, rather than specific information.