What did this people unto thee - It seems if Aaron had been firm, this evil might have been prevented.

And Moses said unto Aaron,.... Having destroyed the calf, and thereby expressed his abhorrence of their idolatry, he examines the principal persons concerned, and inquires into the cause and reason of it, how it came about; and begins with Aaron, though his own brother, with whom along with Hur he had committed the government of the people during his absence; and therefore was justly accountable for such a transaction, which could not have been without his knowledge and consent: no mention is made of Hur, whether he was dead or no is not certain; the Jewish writers say he was, and that he was killed for reproving the Israelites for their wickedness; and it looks as if he was dead, since he was not in the examination, and we hear of him no more afterwards:

what did this people unto thee, that thou hast brought so great a sin upon them? as idolatry is, than which no sin can be greater, it being not only a breach of the first table of the law, but directly against God, against the very being of God, and his honour and glory; it is a denial of him, and setting up an idol in his room, and giving to that the glory that is only due to his name; and Aaron being the chief magistrate, whose business it was to see that the laws of God were observed, and to restrain the people from sin, and to have been a terror to evil doers; yet falling in with them, and conniving at them, he is charged with bringing sin upon them, or them into that; and is asked what the people had done to him, that he should do this to them, what offence they had given him, what injury they had done him, that he bore them a grudge for it, and took this method to be revenged? for it is suggested, had they used him ever so ill, he could not have requited it in a stronger manner than by leading them into such a sin, the consequence of which must be ruin and destruction, see Genesis 20:9 or else Moses inquires of Aaron what methods the people had made use of to prevail upon him to suffer them to do such a piece of wickedness; whether it was by persuasion and artful insinuations, or by threatening to take away his life if he did not comply, or in what manner they had wrought upon his weak side, to induce him to take such a step.

After the calf had been destroyed, Moses called Aaron to account. "What has this people done to thee ("done" in a bad sense, as in Genesis 27:45; Exodus 13:11), that thou hast brought a great sin upon it?" Even if Aaron had merely acted from weakness in carrying out the will of the people, he was the most to blame, for not having resisted the urgent entreaty of the people firmly and with strong faith, and even at the cost of his life. Consequently he could think of nothing better than the pitiful subterfuge, "Be not angry, my lord (he addresses Moses in this way on account of his office, and because of his anger, cf. Numbers 12:11): thou knowest the people, that it is in wickedness" (cf. 1 John 5:19), and the admission that he had been overcome by the urgency of the people, and had thrown the gold they handed him into the fire, and that this calf had come out (Exodus 32:22-24), as if the image had come out of its own accord, without his intention or will. This excuse was so contemptible that Moses did not think it worthy of a reply, at the same time, as he told the people afterwards (Deuteronomy 9:20), he averted the great wrath of the Lord from him through his intercession.

And Moses said unto Aaron, What did this people unto thee, that thou hast brought so great a sin upon them?

32:21 What did this people unto thee - He takes it for granted that it must needs be something more than ordinary that prevailed with Aaron to do such a thing? Did they overcome thee by importunity, and hadst thou so little resolution as to yield to popular clamour! Did they threaten to stone thee, and couldest not thou have opposed God's threatenings to theirs?

32:21-29 Never did any wise man make a more frivolous and foolish excuse than that of Aaron. We must never be drawn into sin by any thing man can say or do to us; for men can but tempt us to sin, they cannot force us. The approach of Moses turned the dancing into trembling. They were exposed to shame by their sin. The course Moses took to roll away this reproach, was, not by concealing the sin, or putting any false colour upon it, but by punishing it. The Levites were to slay the ringleaders in this wickedness; yet none were executed but those who openly stood forth. Those are marked for ruin who persist in sin: those who in the morning were shouting and dancing, before night were dying. Such sudden changes do the judgments of the Lord sometimes make with sinners that are secure and jovial in their sin.