Verse 4 is the summary of verses 1-3. In the first verse we have Alma organizing people to govern the church, in verse 2 we have the positive effect of the ordination, and in verse three the negative aspect of the organization.
When Alma spoke in Zarahemla he spoke to the church. Verses 2 and 3 are clearly referring to those who are not in the church. Therefore we may presume that the organization that Alma put into place was precisely designed to begin a mission to the people of Zarahemla to include them in the church.
From a social perspective, we must understand the picture of Zarahemla that is developing. Beginning with Mosiah and Alma the Elder we had a tacit separation of church and state that became a full blown separation of ideologies. Under Alma the Younger we now have a population that is under the same political aegis, but which follows two different religious paths. In the ancient world, this separation is not as simple as it appears in the modern world, as the conceptual split between religion and the definition of how the world works was not made - there was no science separate from religion.
Thus Zarahemla was home to two incompatible ways of viewing the "reality" of how the world works. This was more divisive that two political parties, a modern situation to which some might compare the Zarahemla problem. To place the conflict into more modern terms, it might be similar to the conflicts between the extremely conservative Muslim countries and Western ideals. While they are worlds apart there is manageable conflict. If those two ideals had significant followers in the same city, the tensions would run high. This is more the picture of Zarahemla that we should understand. There were incompatible ideas of how the world ought to work, and populations upholding each within the city and within the other cities under Zarahemla's umbrella. The tensions might be held in check for a while, but we will begin to see them escalate in the next several years of Alma the Younger's reign.
It is precisely this ideological separation that Alma is trying to heal, and he is trying to heal the division by converting the population to the way of the Lord. In verse 2 it indicates that they do have some success. It is verse 3 that is most important for future events, however. There are those who are not converted. Those who continue to believe in the alternate world view or religion do not leave. They stay in Zarahemla. Future events will clearly indicate that they were not a small number, and that they would become even more influential.