"from the midst of your brothers shall you place over yourself a king": This is a positive commandment.
"You shall not be able to place over yourself a strange man, who is not your brother": This is a negative commandment.
"a strange man": an idolator. (whence it was ruled: A leader is not appointed for the congregation unless his mother is an Israelite.)
"who is not your brother": This is a slave. When (King) Agrippas came to this verse, he would burst into tears, (his father being a non-Jew), whereupon all of Israel said to him: "Fear not, Agrippas; you are our brother, you are our brother," (his mother being Jewish).