Hence, also, we see the error of those who, in comparing the law with the gospel, represent it merely as a comparison between the merit of works, and the gratuitous imputation of righteousness. The contrast thus made is by no means to be rejected, because, by the term law, Paul frequently understands that rule of holy living in which God exacts what is His due, giving no hope of life unless we obey in every respect; and, on the other hand, denouncing a curse for the slightest failure. This Paul does when showing that we are freely accepted of God, and accounted righteous by being pardoned, because that obedience of the law to which the reward is promised is nowhere to be found. Hence, he appropriately represents the righteousness of the law and the gospel as opposed to each other. But the gospel has not succeeded the whole law in such a sense as to introduce a different method of salvation. It rather confirms the law, and proves that everything that it promised is fulfilled. What was a shadow, it has made substance. When Christ says that the law and the prophets were until John, he does not consign the fathers to the curse, which, as the slaves of the law, they could not escape. He intimates that they were only imbued with the rudiments, and remained far beneath the height of the gospel doctrine. 

God The Redeemer (Book 2 of the Institutes) - John Calvin