Samuel Rutherford (c. 1600 – 1661) was a prominent Scottish Presbyterian theologian, pastor, and author. He was selected as one of the four representatives sent by the Scottish church to the Westminster Assembly in London which produced the Westminster Confession of Faith in 1647 as the foundation of the Presbyterian church. In 1644, he published the book that he is most famous for, Lex, Rex (“the law is king”), in response to the common expression by absolutists of the day of Rex, Lex (“the king is law”). Lex, Rex continued the theme of the previous century’s Vindiciae Contra Tyrannos in attacking the idea of absolute monarchy and promoting the covenantal nature of government and the king being equally bound by the law, while at the same time upholding the Christian principle that the civil magistrate and state are biblically instituted. At several points in Lex, Rex, Rutherford touches on the ethnic nature of the law of kin rule in Deut. 17:15.
Deut. 17:15 demands that for the purposes of governance God’s people are to ‘choose one from amongst their brethren’ only and…the fifth commandment layeth obedience to the king on us no less than to our parents… (Q.III, p.4)
…[E]very foal to its dam… [T]he primary law of nations is indeed the law of nature, as appropriated to man…for it is better that my father govern over me than a stranger govern me, and, therefore, the Lord forbade his people to set a stranger over themselves to be their king. The Prelate contendeth for the contrary…but a man’s father was born only by nature subject to his own father, therefore…there is no government natural, but fatherly and marital… (Q.XIII, pp.51-52)
God hath made them heads of the tribes and princes of the people…it is well said that he the king is a son to them, and they, his maker… What the king doth as king, he doeth it for the happiness of his people. The king is a relative. (Q.XXV, pp.120-124)
you may indeed set a king over you whom the Lord your God will choose. One from among your brothers you shall set as king over you. You may not put a foreigner over you, who is not your brother.
Isn’t it funny how the modern church “discovered” that Deut. 17:15 is actually talking about religion and not ethnicity only after it had completely succumbed to cultural Marxism? Historical Christianity held the opposite view.