This is indeed a very important story. I think we too often overlook the fact that if not for the intervention of Moses, God himself would have completely destroyed the Hebrews during their Exodus from Egypt. If not for Moses, they would not exist today, having been obliterated by their own God.
This shows us that God is not all merciful, nor is he all knowing. He can be influenced by both anger and sentimentality, and his love is very conditional.