Charles Ellicott Commentary Nehemiah 10:38

"And the priest the son of Aaron shall be with the Levites, when the Levites take tithes: and the Levites shall bring up the tithe of the tithes unto the house of our God, to the chambers, into the treasure-house." — Nehemiah 10:38 (ASV)

The son of Aaron. —Consult Numbers 18:22-26, which gives the reason for the distinction, so marked here, between the priest, the son of Aaron, and the Levites, the children of Levi. A priest was present when the tithes were gathered in the Levitical cities, to secure their own “tithe of the tithe,” which the Levites then carried to Jerusalem.