What would God have done if He had reacted according to what was fair instead of with grace and mercy?

Les teaches that God shows mercy rather than wrath and judgment. He points to the persecutor and raging religious zealot who hated Jesus of Nazareth, and says that by the grace of God, instead of zapping the man or sending him to eternal doom, God's grace permitted Him to save him and pour out mercy. Les then applies this more broadly: throughout human history, if God had reacted without grace and mercy, according to what was fair, He would have wiped out the human race and wiped out Israel. He illustrates this with Israel demanding that Aaron make a golden calf while Moses was up in the mountain; they danced in lewdness and practiced immorality, and God could have removed them with one thought. Yet God told Moses later in Deuteronomy 33, "I will have compassion on whom I will have compassion, I will have mercy on whom I will have mercy," because He is sovereign and can do whatever He wants to do.