One by one, these disciples would infect the nations with grace. It wasn't a call to take the sword or the throne and force the world to bow. Rather, they were to live the contagious love of God, to woo the nations into a new future.
David, Moses, Saul of Tarsus, these were all people who did terrible terrible things - they were murderers. The Bible would be a lot shorter without grace.
If those of us who believe in God do not believe God's grace is big enough to save the whole world... well, we should at least pray that it is.