But he that did - Intent on his purpose, filled with rage and passion, he rejected all interference, and all attempts at peace. It is usually the man that does the injury that is unwilling to be reconciled; and when we find a man that regards the entreaties of his friends as improper interference, when he becomes increasingly angry when we exhort him to peace, it is usually a strong evidence that he is conscious that he has been at fault. If we wish to reconcile parties, we should go first to the man that has been injured. In the controversy between God and man, it is the "sinner" who has done the wrong that is unwilling to be reconciled, and not God.
His neighbour - The Jew with whom he was contending.
Who made thee - What right have you to interfere in this matter? The usual salutation with which a man is greeted who attempts to prevent quarrels.

But he that did his neighbour wrong,.... Who seems to be the same person whom Moses had defended the day before; and, according to the Jews, must be Dathan (a): the same
thrust him away; from them, when he went to part them, and persuade them to be good friends:
saying, who made thee a ruler and a judge over us? which was very ungrateful, if he was the man he had delivered the day before; and very impertinent, since he did not take upon him to rule and judge, but only to exhort and persuade to peace and brotherly love: the language suits with the spirit of Dathan or Abiram; Numbers 16:3 This is thought to be said to him by way of contempt of him, as being a very young man: the words are thus commented on in one of the ancient commentaries of the Jews (b),
"R. Judah says, Moses was twenty years of age at that time: wherefore it was said to him, thou art not yet fit to be a prince and a judge over us, seeing one of forty years of age is a man of understanding. And R. Nehemiah says, he was forty years of age; See Gill on Acts 7:23 and it was said to him, truly thou art a man, but thou art not fit to be a prince and a judge over us: and the Rabbans say, he said to him, art thou not the son of Jochebed, though they call thee the son of Bithiah? and dost thou seek to be a prince and a judge over us? it is known concerning thee what thou didst to the Egyptian.''
(a) Targum Jonah. in Exod. ii. 14. Debarim Rabba, sect. 2. fol. 237. 1. (b) Shemot Rabba, ib.

Who appointed thee - "Under the presence of the want of a call by man, the instruments of God are often rejected."