This is the essential parallel that Alma wants to make clear. The priests who received the priesthood were sanctified, eschewed sin, were cleansed through the Atonement (or the promise of the coming Atonement) and were able to enter into the rest of God.
Alma uses that example as a model for the current Ammonihahites, and exhorts them to repent, so that they too may "enter into that rest." Alma is not necessarily implying that all there should become priests, but rather that the process of repentance and acceptance of the mission of the Atoning Messiah is critical to receiving the blessings of the rest of the Lord.
Vocabulary: Fruits meet for repentance are those which are equal to the task. The word "meet" is a variation of an ancient word for "measure." We may also see it in the form mete from which more directly we receive words of measuring, such as metric.