Or HaChaim on Exodus 23:21/אור החיים על שמות כ״ג:כ״א

1 השמר מפניו, "Take heed of him, etc." In this verse G'd defines our relationship with this angel as involving both a positive and a negative commandment. The negative commandment is contained in the words השמר מפניו, just as in all other places where the word השמר introduces a negative commandment. The positive commandment is contained in the words ושמע בקולו, "listen to his voice."

2אל תמר בו, "do not rebel against him;" Here too the Torah contains a moral/ethical lesson in addition to the plain meaning of the words. The Torah hints that exchanging good for evil will result in the king being replaced by a slave and the maidservant inheriting the authority of the mistress (compare Proverbs 30,23). The message is that when Israel is sinful it will be subject to an attribute of G'd which takes "revenge" rather than elevates sins to a lesser level. The angel under discussion is not authorised to do this. When the Torah speaks of כי שמי בקרבו, this means that man has forfeited the presence of G'd in his midst because of his sins, and G'd's former presence within man is now centred in that angel. Sanhedrin 38 teaches that the numerical value of מטטרון, Mattaron (the angel G'd appointed in charge of running the universe), is the same as that of his Master, G'd's attribute שדי,=314. When man sins, G'd no longer considers Himself as "his" G'd, i.e. שדי. This is the mystical dimension of Isaiah 19,5: ונהר יחרב ויבש, "the river will fail and dry up." The intelligent reader will comprehend that the words כי אם שמוע תשמע בקולו, "if you will surely listen to his voice," sounds as if G'd is speaking about a third person, whereas the Torah continues: ועשית את אשר אדבר, "and you will do what I say." G'd was careful not to say אשר ידבר, "which he will say," in order to remind us that His name is in the midst of the Jewish people.