Love this quote from John Bunyan, which Mark Henderson posted in the comments to my previous post:
He that is dark as touching the scope, intent and nature of the law, is also dark as touching the scope, nature and glory of the gospel. … I say, therefore, if thou wouldst know the authority and power of the gospel, labour first to know the power and authority of the law. For I am verily persuaded that the want of this one thing, namely, the knowledge of the law, is the one cause why so many are ignorant of the other. … Again, that man that doth not know the nature of the law, that man doth not know the nature of sin; and that man that knoweth not the nature of sin, will not regard to know the nature of a Saviour.