I just read a really, really good comment on a messageboard. It was a thread about good works and obedience, and how God can require anything of us, and yet Christ still wholly fulfill the justice of God on our behalf.

The response was that our obedience is not a requirment to satisfy justice. Our obedience doesn’t have anything to do with paying God, since it was a requirment in place before The Fall. Adam was in a favorable position with God, and so his obedience was not to gain God’s favor, nor are good works/obedience made to make payment to God for wrong doing. Rather, God’s requirment of us has to do with His character, and man being made in His image, to reflect His character.