Matthew Poole and continuators on 1 Chronicles 27:3

3 Of the children of Perez , was the chief of all the captains of the host for the first month.

Or, of Pharez, of the Posterity of Iudah, Gen. 46. 12. This seems to be understood of Iashobeam, and to be mentioned as a reason why he was the Chief, &c. and the verse may be rendred thus, He was (which is easily understood out of the foregoing words) of the children of Perez (and consequently of the Tribe of Iudah, to which the Pre-eminence belonged, and of which Iudah was) and he was (or, therefore he was) the Chief (to wit, in Dignity and Precedency, though not in Power and Authority, for these captains were equal in Power, and Ioah was their General) of all the Captains of Host (whose several Names here follow) and was for the first month. Therefore he was first in Order and was Captain for the first month.