Exodus 32:10

Let me alone What did Moses, or what could he do, to hinder God from consuming them? When God resolves to abandon a people, and the decree is gone forth, no intercession can prevent it. But God would thus express the greatness of his displeasure, after the manner of men, who would have none to intercede for those they resolve to be severe with.

Thus also he would put an honour upon prayer, intimating, that nothing but the intercession of Moses could save them from ruin.