Why does God get to decide whom He shows mercy to?
God decides whom to show mercy because He is sovereign. He can do whatever He wants and does not have to ask anyone. Scripture declares, 'I will have compassion on whom I will have compassion, I will have mercy on whom I will have mercy.' His mercy flows from His own will, not human merit.
Les explains that God is sovereign, so He can do whatever He wants and does not have to ask anybody. When Israel or mankind reached the point where God should have just zapped them, He retreated into His sovereignty and by grace poured out mercy. For example, when Israel worshiped the golden calf, God could have wiped them out with one thought, but He told Moses in Deuteronomy 33 that He will have compassion on whom He will have compassion and mercy on whom He will have mercy. Les teaches that God did the same with Saul of Tarsus on the road to Damascus: He could have zapped him, but instead He retreated into sovereignty, said He would have compassion on that man because He is God, and spared and saved him by His grace. This matches 1 Corinthians 15:10, where Paul says it was by the grace of God that he is what he is.