Basically God said the same thing to Noah / Abraham / Moses:
“Stand back, I’m gonna kill ‘em. You’re safe, but they’re dead meat.”
Noah said, “You go, God! I'll build that ark just like you told me so me and mine will be safe while those bastards drown.”
Abraham said, “Ah, c’mon, God. Surely you won’t kill ‘em if you find fifty nice guys in town? Forty? Thirty? Twenty…?”
But Moses said, “God, please don’t do that. What will people say? (You can’t be trusted, that’s what they’ll say.) You said they were your people, you said I was to lead them. How can I do that if you won’t stay with us?”
Note the different attitudes.
Noah acts like a belligerent old drunk. “Yeah, screw them. You ‘n’ me, best buds f’rever, right, God?”
Abraham acts like a nice guy, but it’s still pretty clear that in his Weltanschauung the not-so-good folk of Sodom & Gomorrah represent “them”, not “us”. He’s more than happy to make an intellectual argument in their favor that doesn’t cost him a drachma, but stand with them? No way-a, Hosea.
Only Moses puts his ass (or perhaps camel) on the line, identifying with the very people God has just pronounced a hate-on for. For all he knew, God’s next words were going to be: “Well, if that’s your attitude, fine. You can go to hell or Texas for all I care.”
But God doesn’t. Instead, he appears to relent and stay with the Israelites -- stiff-necked, back-sliding yutzes that they were.[1]
Moses is demonstrating what is arguable the first expression of “Do unto others as you would have them do unto you” in the Bible.[2]
I think we are all agreed that if we felt we were on God’s shit-list, we’d want somebody to do anything & everything they could to save us, up to & including calling in personal favors from the Most Holy.
That’s what Moses did.
And to people who just a short while earlier hated him, betrayed him.[3]
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[1] God being transcendent, He knew this outcome of this scenario long before Abram was called out of Ur. But Moses couldn’t grasp God’s transcendent nature, so the idea of God changing His mind or altering a prophecy were not unthinkable to him.
[2] Joseph was the first moral man, but his morality was confined to his own family whom he spared and forgave so as to be a blessing to his father. Moses was not only defending people he didn’t even know personally, but people who were actively and continuously working against him.
[3] Mo’ wasn’t perfect, not by a long shot; he left a mountain of corpses behind, but still, the overwhelming majority of Israelites he got off the hook.