Helaman and his brethren take up the task of preaching, and they were successful. This led to the renewal of the church, and to the rule of law. By noting both the church and the judges, Mormon is simply noting that things are returning to stability, and to a stability that reflected righteous principles.
Because the people were becoming more righteous, they “began to prosper again in the land, and began to multiply and to wax exceedingly strong again in the land. And they began to grow exceedingly rich.” That is, of course, just as the covenant of the land had promised.