These verses parallel the ideas in verses 18 through 21. The imagery depicts standing before God in the final judgment without having become clean. The reason for this emphasis is that becoming clean requires the atoning sacrifice of the coming Messiah. Alma is declaring that they will not be able to stand clean before God in the final judgment, save it is through the atoning mission of the Messiah. The implication, once again, is that at least some of them have rejected that belief.
It is not clear why Alma declares that some of the congregation might be considered murderers or “guilty of all manner of wickedness.” Under Nephite law, they would have been brought to justice had they actually committed murder. However, if Alma is speaking of tendencies, then the tendency of those who rejected the understanding of the coming Messiah also typically followed the trends of the greater society. One of the ways that the large Mesoamerican society became richer was through conquest, and such conquests are often characterized as murders and robbers in the Book of Mormon.