God has chosen the foolish things.

I was told that silver stands for redemption because there is no silver in heaven.  It represents the miracle of savation, that the angels can only look on in awe.  They were created without the need for redemption, so can not experience it.  Redemption only occurs on the earth, in human flesh. It  also speaks of the thirty pieces of silver that Judas was paid for the life of Jesus, this was the going price for the purchase of a slave...the monetary value of a human life in biblical times. It is also a beautiful, electrically conductive metal which must be periodically cleansed from tarnish.  The process of polishing that is required to keep silver "silver" is representative of the process of restoration that takes place in the heart of humankind.