Albert Barnes Commentary 1 Chronicles 23:27

"For by the last words of David the sons of Levi were numbered, from twenty years old and upward." — 1 Chronicles 23:27 (ASV)

By the “last words of David,” some understand a historical work on the latter part of his reign, likely drawn up by Gad or Nathan (Compare 1 Chronicles 27:24; 1 Chronicles 29:29). Others suppose that he left behind a work containing directions for the service of the sanctuary.