Exodus 18:21

Able men - The qualifications are remarkably complete, ability, piety, truthfulness, and unselfishness. From Deuteronomy 1:13, it appears that Moses left the selection of the persons to the people, an example followed by the Apostles; see Acts 6:3.

Rulers of thousands ... - The numbers appear to be conventional, corresponding nearly, but not exactly, to the military, or civil divisions of the people: the largest division (1,000) is used as an equivalent of a gens under one head, Numbers 1:16; Numbers 10:4; Joshua 22:14.

The word “rulers,” sometimes rendered “princes,” is general, including all ranks of officials placed in command. The same word is used regularly on Egyptian monuments of the time of Moses.