What does Psalm 90:13 mean?

Moses asks the Lord to turn from His justified anger and to have pity on His people. He wondered how long the Lord would direct judgment toward His sinning people.

The book of Jonah pictures both the Lord's anger and His pity. God told Jonah to go to Nineveh and cry against its evil, but Jonah disobeyed the command. He boarded a ship bound for the opposite direction. But after Jonah repented from the belly of the great fish that swallowed him, the Lord graciously recommissioned him. When the city of Nineveh received Jonah's message, repentance broke out from the highest level of government to the lowest level of society. As a result, the Lord responded with pity and compassion. Jonah 3:10 reports: "When God saw what they [the people of Nineveh] did, how they turned from their evil way, God relented of the disaster that he said he would do to them, and he did not do it."

Micah 7:18–19 pictures God as pardoning iniquity, withholding His anger, delighting in steadfast love, compassionate, treading iniquities underfoot, and casting all Israel's sins into the depths of the sea. It was to this God that Moses appealed for pity.