3 Nephi 5
It is amazing to me that every living Nephite knew that Christ had come and yet within 8 years the wickedness among them would be so great that their government was utterly destroyed.
It is interesting that Mormon notes that the church formed by Alma at the waters of Mormon was the first church to be among the people after their transgression. I guess that prior to that church forming they had Nephi and those priests ordained by him to lead the people, but once they transgressed the role or title of priest was more a social position than a truly religious one. Until Alma formed the church they had prophecy by individuals who would call their fellow men to repentance, but they had no organization of the church nor official delineation between those in the church and those outside of it.