Please pardon the iniquity of this people, according to the greatness of your steadfast love, just as you have forgiven this people, from Egypt until now.
At the very cusp of entering the Promised Land, Israel rebelled against the Lord. The spies sent out to scout out the land in advance returned with a mixed review. Ten of the group of twelve were negative in outlook, focusing on only the obstacles to gaining the good gift from God. Two of them, Joshua and Caleb, were enthusiastically encouraging and exhorted the people to have faith, confident that God would lead the nation beyond the mere obstacles of armies and giants.
But any hint of negativity will result in a nearly universal leadership principle: People will quickly turn tentative leadership into rebellion. And as they spoke against the Promised Land, the nation spoke against the Lord. And God was finally through with a nation of grumblers. He informs Moses that He would like to end Israel right there in the desert and make a new covenant with Moses and his descendents, sort of a generational "do over". The grumbling must stop. Moses respectfully and successfully intercedes for a doomed generation.
God then reveals a gracious plan that both punishes a faithless generation and protects His promises to bring Israel into the Promised Land. An entire generation must die, wandering the desert wastes for forty years. When the last corpse of a faithless and complaining generation is buried in the Sinai sand, then God would lead their children into Canaan. It was Moses' faithful intercession that gave a new generation a grace that their parents refused to accept from God.
I am warned about faithless complaining. The example of the Exodus generation reminds me of this each time that I read it. It also shows me the faithful love of God Who will forgive, even as sinful consequences remain.