Commentaries:
Barnes' Notes
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.
Other Barnes' Notes entries containing Exodus 18:21:
Leviticus 24:12
Numbers 1:5-16
Deuteronomy 1:9-15
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