The theologian Karl Barth was once asked by another Christian if he could name the date and time that he had been saved, the implication being that if he couldn't name that moment of conversion, it hadn't really happened. In response to this litmus test, Dr. Barth answered: "I know when it happened. At 3:00 p.m. on that first Good Friday."
We remember that Friday called "good" because it is the basis on which we meet the world's sorrow with God's love. Because the cross is the healing of the world.