John Calvin on Jeremiah 29:25

He afterwards mentioned the priest and all the priests The word priest, in the singular number, meant the high-priest: then the priests were not only those descended from Aaron, but all the Levites. There was the high-priest, and then the descendants of Aaron were the chief, and, as it were, the colleagues of the high priest; but the Levites were an inferior order, though here by the priests he means also the Levites.