When the LORD tells Moses He's fed up with "your people," Moses always implores the LORD to remember His promises to His people. And the LORD relents.
The LORD is not fickle, yet everything asserted by the inspired authors or sacred writers of Scripture must be held to be asserted by the Holy Spirit. So what might He have been up to in these stock exchanges with His chosen servant?
It struck me yesterday that the Divine threats against the Hebrews force Moses to take a stand, the stand of pleading for them before God. Each time he pleads for them before God, he strengthens the bond he has with the people he leads -- with what God calls "your people" when He's angry with them, but "My people" when He's pleased.
So this is not just a pro forma conversation -- "One of these days, POW, right in the kisser!," "Now, now, calm down," "Oh, all right." It is a ritual by which God, Moses, and the Israelites are all drawn deeper into a relationship of love. God begins the ritual, but it is up to Moses to continue it.
But suppose he didn't. Suppose he said, "You're right, LORD. They are a stiff-necked people, and I would love it if Your wrath consumed them. Then you could make of me a great nation." What if he called God's bluff?
Notice that the Church puts the reading of their ritual conversation sparked by the golden calf on the same day as the Gospel reading of the Parable of the Prodigal Son. In that parable, it was the task of the older brother to assume the role of Moses, to intercede with his father on behalf of the younger son. He failed in this rather spectacularly, and wound up harming only himself.
So while the Biblical stories that portray God as capricious and always threatening to find a better people make for dramatic reading (or at least they could, if we paid attention), I don't think God's plan of salvation was really dancing on a knife edge all those years. His plan is sound, secure, and unchanging; the drama comes from our own fickleness: Will we, individually and communally, choose life, or will we choose death?