C. F. Keil and Franz Delitzsch on 2 Chronicles 31:17

2Ch 31:17 2Ch 31:17 contains a parenthetic remark as to the catalogues. ואת, as nota accus., serves here to emphasize the statement which is added as an elucidation (cf. Ew. §277, d): “But concerning the catalogue of the priests, it was (taken, prepared) according to the fathers'-houses; and the Levites, they were from twenty years old and upwards in their offices in their courses.” All the duties were discharged by several courses. On the age fixed on, see 1Ch 23:27.