Also, here's an article that he wrote. Here's a snippet.
The meaning of the collapse of this bridge is that John Piper is a sinner and should repent or forfeit his life forever. That means I should turn from the silly preoccupations of my life and focus my mind’s attention and my heart’s affection on God and embrace Jesus Christ as my only hope for the forgiveness of my sins and for the hope of eternal life. That is God’s message in the collapse of this bridge. That is his most merciful message: there is still time to turn from sin and unbelief and destruction for those of us who live. If we could see the eternal calamity from which he is offering escape we would hear this as the most precious message in the world.