(13) And he said: ‘Oh Lord, send, please, by the hand of him whom You will send.’ (14) And the anger of the Eternal was kindled against Moses, and He said: ‘Is there not Aaron your brother the Levite? I know that he can speak well. And also, look, he comes to meet you; and when he sees you, he will be glad in his heart. (15) And you shall speak to him, and put the words in his mouth; and I will be with your mouth, and with his mouth, and will teach you what you shall do. (16) And he shall be your spokesman unto the people; and it shall be, that he shall be your mouth, and you shall be to him a god. (17) And you shall take in your hand this rod, and with you shall do the signs.’
And God was angry. Rabbi Yehoshua ben Karcha says: every time God's anger is mentioned in the Torah, it is mentioned with a lasting mark, but this one has no lasting mark mentioned with regards to it. Rabbi Yosi said: This one to has a lasting mark, "Is there not Aharon your brother, the Levite...", who has been destined to be a Levite and not a Kohen, but the Kehunah I had said would come from you; from now onward it will not be so, but rather he will be the Kohen, and you the Levite, as it said: "But as for Moses, the man of God, his sons will be reckoned among the tribe of Levi." (Chronicles I 23:34)
And he will see you, and rejoice in his heart. Not as you think, that he will resent you because you are going up in greatness, and from this, Aharon will merit to wear the Choshen, which is worn over the heart.
(א) ויחר....וטעם הלוי שכן היה נודע בישראל הנביא הלוי. כי היה בהם אחרים ששמם כשמו. ודבר זה אין זה גרעון למשה רק מעלה גדולה כי אהרן יהיה דומה לפה שיוציא דבור הנשמה שאינו נראית כמו המלאכים שאינם נראים כי אינם גוף. והנה ידמה משה כמעלת המלאך וזהו ואתה תהיה לו לאלהים.
And reason for "Levite" is that Aharon was known among Israel as a the Levite prophet. Because there were among them other ones whose name were like his. And this is not a rebuke against Moses, only an increase in his greatness, for Aharon would be like a mouthpiece, who would put forth an utterance of the soul, which is not visible, like with ma'lachim which are not visible since they have no body. And, look, Moses would be like the level of a mal'ach, and this is the meaning of "You will be like a God for him."
With your mouth to teach you what you are to say to Pharaoh. For up to this point, God has said that Aharon would only speak to the people, as it says: "And he will speak to the people," but to Pharaoh Moses would speak, which could be out of honor for the king. And finally, Moses responds: "yes I am of uncircumcised lips! How would Pharaoh listen to me?" (Shemot 6:30), and God allowed that Moses would not speak to Pharaoh, and so he raises up Moses, and therefore God said, "See, I am placing you as god before Pharaoh, and Aharon your brother will be your prophet." (Shemot 7:1): And the reason is that "and with his mouth" so that the words of his mouth are graceful to those who hear.
(1) הלא אהרן אחיך? If it had been My intention to appoint someone naturally suited for the task, there is your brother Aaron, the Levite, undoubtedly a wise man as are all his brothers the Levites. (2) כי ידעתיו כי דבר ידבר הוא, for I am well aware that he is an excellent speaker without needing training, וגם הנה הוא יוצא לקראתך וראך ושמח בלבו, and although he is on the way to meet you out of respect for you and your elevation to an even higher status than his own, he will undoubtedly be happy to serve as your interpreter full-heartedly.