"Now it came to pass that Alma began to deliver the word of God unto the people first in Zarahemla and thence throughout all the land." Alma did not give this same speech everywhere he went, but he delivered the word of God at each location. He referred to his obligation to cry repentance and preach the coming of Christ as a duty under the holy order of the Son of God—in other words, a priesthood responsibility. He went on to speak for this same purpose in in Gideon (6:7), in Melek (8:3), and probably elsewhere as well.
As he spoke in Zarahemla in Alma 5, he was speaking to a somewhat ambivalent audience. There was a dilemma there, even an "awful dilemma" (Alma 7:3). There were some people who were righteous and very good, and some people who were not. In Gideon, however, he was speaking to a very righteous audience. Then the next place he went to was Ammonihah. So there was a wide range of people and audiences to whom he spoke. While the bottom-line message to each was very similar, the way he delivered it, how he talked, and what points he emphasized in each case were very different. As he delivered the word of God throughout all the land, he adapted his teachings and testimony to various needs and circumstances while he kept the core message the same.
Ed J. Pinegar and John W. Welch, Experiencing a Mighty Change of Heart: Alma’s Guide to a Deep, Lasting Conversion (American Fork, UT: Covenant Communications, 2020), 2: "For at least twenty-five years, Alma spoke to countless people, teaching the doctrines of Christ and preaching repentance. He spoke encouragingly about the Atonement of Christ to the righteous people in Gideon. He called the wicked people in Ammonihah to repentance and deliverance, and in a last-ditch effort to turn them away from their Nehorite ways, Alma spoke to them urgently about spiritual death, probation, and the plan of redemption, followed by his testimony about the high priesthood after the holy order of the Son of God."