The spirit confirmed to Alma that this people were not in a state of apostasy, as were many in the city of Zarahemla. As Alma sets up the contrast between the two peoples in the different locations, he points out the particular apostasies that had developed in Zarahemla. This gives us a picture of what was happening, that the sermon itself did not mention. While we can read the information for historical purposes, Alma presented it in order to congratulate the people in Gideon for not falling into those traps, clearly because they were also ideas and actions that were available to them in their greater environment.
What were the sins in Zarahemla? Alma has preached about the sin of pride and of lifting oneself above others in his sermon in Zarahemla. What is added here is “I trust that you do not worship idols.” The only reason for saying this to the people in Gideon is that it was possibly true of many in Zarahemla. Thus, we have confirmation that a competing religious idea had entered. It is highly likely that it stemmed from both other available beliefs within the greater religion, and from the inheritance of the people of Zarahemla from before the arrival of the Nephites, or from the people of Zarahemla during the time when “they denied being of their Creator” (Omni 1:17).
Most importantly, Alma admonishes the people in Gideon to further separate themselves from the wickedness of Zarahemla by understanding that “there is one thing which is of more importance than they all.” That is the coming of the Messiah. In Alma’s Zarahemla sermon he noted that they had drifted from their understanding of the coming Messiah. That is, in Nephite religion, the thing “of more importance than they all.” Therefore, Alma encourages the people in Gideon to continue in their belief in that coming Messiah, and to understand that “the time is not far distant.” They are to prepare themselves just as we modern readers are to be prepared for the next time that the Redeemer comes to the world.