1 Chronicles 23

As David grows old, he makes Solomon king and numbers the Levites from age thirty and upward. He assigns Levites to temple service, officers and judges, gatekeeping, and music. The chapter traces the families of Gershon, Kohath, and Merari and explains that because the ark will have a permanent resting place, some earlier wilderness-era carrying duties will no longer be needed. David later counts Levites from age twenty for the new service structure.