וַיֶּֽחָלְקֵ֥ם דָּוִ֖יד מַחְלְק֑וֹת (ס) לִבְנֵ֣י לֵוִ֔י לְגֵרְשׁ֖וֹן קְהָ֥ת וּמְרָרִֽי׃ (ס)
And David divided them into courses according to the sons of Levi: Gershon, Kohath, and Merari.
Read midrashic interpretation of I Chronicles 23:6: and classical rabbinic exegesis.