“The truth of Christianity cannot be established by the intellect unless an important part of the argument is based upon the fact of sin which is revealed by the law of God; the beauty of Jesus, which attracts the gaze of men, cannot be appreciated without a knowledge of the holiness upon which it is based; the companionship of Jesus is possible only to those who say first, in deep contrition; 'Depart from me; for I am a sinful man, O Lord'; the example of Jesus is powerless to those who are in the bondage of evil habit, and it is not even a perfect example unless He be the divine Redeemer that He claimed to be. The true schoolmaster to bring men to Christ is found, therefore, now and always in the law of God— the law of God that gives to men the consciousness of sin.
A new and more powerful proclamation of that law is perhaps the most pressing need of the hour; men would have little difficulty with the gospel if they had only learned the lesson of the law. As it is, they are turning aside from the Christian pathway; they are turning to the village of Morality, and to the house of Mr. Legality, who is reported to be very skillful in relieving men of their burdens. Mr. Legality has indeed in our day disguised himself somewhat, but he is the same deceiver as the one of whom Bunyan wrote.
'Making Christ Master' in the life, putting into practice 'the principles of Christ' by one’s own efforts these are merely new ways of earning salvation by one’s own obedience to God’s commands. And they are undertaken because of a lax view of what those commands are. So it always is: a low view of law always brings legalism in religion; a high view of law makes a man a seeker after grace."
(J. Gresham Machen, What Is Faith?, p. 141-142)