Why doesn't God need to pour out His mercy again?

Les explains that the request “God be merciful to me, a sinner” is not appropriate today because God has already poured out His mercy. He did that at the cross, and asking for it again is a double take—saying God had better do it again. Les says no, He doesn’t have to do it again, because He has already poured out all the mercy of a sovereign God. Instead, we appropriate that mercy by faith, saying, “Yes, Lord, I know Your mercy was poured out; now I believe it; I appropriate it; it’s mine.” This makes all the difference when we understand what God has already accomplished at the cross on our behalf. Les then returns to Romans 9, where Moses was flat on his face after the golden calf. God told Moses, “I will have compassion on whom I will have compassion, and I will have mercy on whom I will have mercy, because I am sovereign. I am the final authority.” Verse 16 then says it is not of him that willeth, nor of him that runneth, but of God who showeth mercy.