1 Chronicles 9:2

Now the first inhabitants - This is spoken of those who returned from the Babylonish captivity, and of the time in which they returned; for it is insinuated here that other persons afterwards settled at Jerusalem, though these mentioned here were the first on the return from the captivity. Properly speaking, the divisions mentioned in this verse constituted the whole of the Israelitish people, who were, ever since the days of Joshua, divided into the four following classes:

1. The priests.

The Levites.

The common people, or simple Israelites.

4. The Nethinim, or slaves of the temple, the remains of the Gibeonites, who, having deceived Joshua, were condemned to this service Joshua 9:21 , etc. In David's time it is probable that other conquered people were added, as the successors of the Gibeonites were not sufficient to perform all the drudgery of the temple service.