Why?

We are finishing up our reading of the Book of John at dinnertime.  Tonight we read about Mary coming to the tomb and finding it empty.  

It is very important, to me, that my children know why they believe what they believe.  The more they know why, the better they will be able to defend their faith.  (I Peter 3:15)  So tonight I asked my son, "Why did Jesus have to die?"

Jesus was not a martyr that died because He was arrested and then miraculously rose from the dead.  He willingly gave up His life, but why?  The obvious answer is to save the world.  But why did He have to die to save the world?  I think this is something many of us take for granted, but can you answer why, and know why you believe it?

I would like to hear your thoughts.