I am not sure where to say the gift of mercy began. Did it begin with creation? Did it begin at the fall? Did it begin when the angel announced to Mary that she would give birth to a Savior? Did it begin when Jesus was born or did it begin on the cross?
I am not really sure that it matters. What is important, is that we recognize this gift, and give God an immeasurable thanks for the fact that because of the fall, we all deserve death. We all have sinned, we have all fallen short, but we all have access to this gift of mercy (freedom from death) through Jesus.
We deserved condemnation. Our condemnation was removed. Mercy. Unfathomable really.