It is equally true that adoption lays on one the abiding obligation to keep the law, as the means of pleasing one's newfound Father. Adoption puts law-keeping on a new footing: as children of God, we acknowledge the law's authority as a rule for our lives, because we know that this is what our Father wants. The sins of God's children do not destroy their justification or nullify their adoption, but they mar the children's fellowship with their father. 

packer, knowing god, pg 223