Exodus 32:30

You. Many who had not been slain, had followed the bad example, and Aaron, in particular, had brought upon them a most heinous sin, ver. 21. Yet on account of their repentance, they were not subjected to immediate punishment; but they were visited afterwards, ver. 34. Though God was appeased, (ver. 14,) so as not to destroy the whole multitude, Moses thought it a very arduous task to obtain a full reconciliation, notwithstanding the exemplary vengeance he had taken of the ringleaders. Hence he addresses himself to God with the greatest humility, and with such earnestness as scarcely seems justifiable, if we understand that he put his own eternal salvation at stake. But he makes an impossible supposition, or proposal, which he knew God would not admit, to extort as it were the requested favour. As he is willing to die for his people, God pardons them for his sake. (St. Augustine, q. 147, &c.) (Haydock)