Deuteronomy 17:15

Thou shalt set him, i.e. appoint, or install. If you will choose a king, which I shall suffer you to do, I command you to mind this in your choice. Whom the Lord shall choose, approve of, or appoint. So it was in Saul, and in David. God reserved to himself the nomination both of the family and of the person. See 1 Samuel 9:15, 1 Samuel 10:24 1 Samuel 16:12 1 Chronicles 28:4,5. From among thy brethren; of the same nation and religion; partly because such a person was most likely to maintain true religion, and to rule with righteousness, gentleness, and kindness to his subjects; and partly that he might be a fit type of Christ, their supreme King, who was to be one of their brethren. Mayest not set a stranger over thee, to wit, by thy own choice and consent; but if God by his providence and for their sins should set a stranger over them, they might submit to him, as appears from Jeremiah 38:17 Ezekiel 17:12 Matthew 22:17.