John Wesley on Deuteronomy 17:15

Thy God shall chuse - Approve of, or appoint. So it was in Saul and David. God reserved to himself the nomination both of the family, and of the person. Thy brethren - Of the same nation and religion; because such a person was most likely to maintain true religion, and to rule with righteousness, gentleness, and kindness to his subjects; and that he might be a fit type of Christ their supreme king, who was to be one of their brethren.