Deuteronomy 17:14

14.When thou art come unto the land. In this passage God sets forth the merits of that sacerdotal kingdom, of which mention is made elsewhere; for, since the splendor of the royal name might dazzle their eyes, so that they should forget that God retained the sovereignty over them, they are thus early admonished how unjust it would be if the majesty of God should be diminished by the rule of a mortal man. In sum, the power of kings is here put beneath that of God; and kings themselves are consecrated unto obedience to Him, lest the people should ever turn to ungodliness, whatever change of government might take place. But although under the judges religion was often subverted, yet it was not without a cause that a special law was enacted with respect to kings, because nothing is more likely than that earthly pomps should draw men away from piety. Now we understand the design of God in this matter, let us proceed to examine its several parts. He passes over (as I have said) all the intermediate time until the beginning of the kingdom, because this new state of things brought with it an increase of danger: for as long as the judges were in power, their different form of government separated the Jews from heathen nations. All the surrounding neighbors were subject to kings; and God always retained the preeminence, whilst He raised up judges from amongst the people; but when they began to choose kings for themselves, they were so mixed up with the Gentiles, that it was easy for them to fall into other corruptions. For the very similarity (of their governments) united them more closely; wherefore, it is expressly said, When thou shalt set a king over thee “like as all the nations that are about” thee. For God signifies that the example of the nations would be an evil snare to them, that they should desire to have a king, and thus their condition would in future be identical, though by divine decree it had been distinct. In short, their rebellion is here indirectly condemned, when God foretells that they would wantonly shake off their yoke; as indeed actually took place, when they rejected Samuel, and tumultuously required a king. On which point God elsewhere complains that He was despised. But the question arises, how these two things can be reconciled, that kings should reign over them from the lust or foolish desire of the people, and yet that the kingdom was the chief glory of the people, a special pledge of God’s favor, and consequently of their welfare and full felicity. The prophecy of Jacob is well known,

"The scepter shall not depart from Judah, — until Shiloh come.” (Genesis 49:10.)

Whence it appears that a king was promised to the children of Abraham as an inestimable blessing. Why, then, does not God declare Himself its author? I reply that, although it was God’s design from the beginning to set up David as a type of Christ, yet, because their unseemly haste disturbed the order of things, the commencement of the kingdom is ascribed to the people’s fault, when they were impelled by their perverse emulation to wish to be like the Gentiles. God appears then to have designedly censured their wilfulness, as if He had said, “Although by appointing a king, you approach more nearly to the Gentiles, beware lest your perverse desire should altogether turn you away from true religion.