Of the sons of Kohath ... — Kohath appears to have been the second son of Levi (Numbers 3:17), but the Kohathites here…

There were three families, those of Kohath, Gershon, and Merari, and to each of these families a different service was allotted.

1. They …

Take the sum of the sons of Kohath from among the sons of
Levi
They were to begin wit…

The middle-aged men of the tribe of Levi, all from thirty years old to fifty, were to be employed in the service of the tabernacle. The service of …