Christ is a sufficient Saviour; but what has He done, and what will He do, not merely for the men who were with Him in the days of His flesh, but for us? How is it that Christ touches our lives?
The answer which the Word of God gives to that question is perfectly specific and perfectly plain. Christ touches our lives, according to the New Testament, through the Cross. We deserved eternal death, in accordance with the curse of God’s law; but the Lord Jesus, because He loved us, took upon Himself the guilt of our sins and died instead of us on Calvary. And faith consists simply in our acceptance of that wondrous gift. When we accept the gift, we are clothed, entirely without merit of our own, by the righteousness of Christ; when God looks upon us, He sees not our impurity but the spotless purity of Christ, and accepts us “as righteous in His sight, only for the righteousness of Christ imputed to us, and received by faith alone.”
That view of the Cross, it cannot be denied, runs counter to the mind of the natural man. It is not, indeed, complicated or obscure; on the contrary it is so simple that a child can understand, and what is really obscure is the manifold modern effort to explain the Cross away in such fashion as to make it more agreeable to human pride. But certainly it is mysterious, and certainly it demands for its acceptance a tremendous sense of sin and guilt. That sense of sin and guilt, that moral awakening of a soul dead in sin, is the work of the Spirit of God; without the Spirit of God no human persuasion will ever bring men to faith. But that does not mean that we should be careless about the way in which we proclaim the gospel: because the proclamation of the message is insufficient to induce faith, it does not follow that it is unnecessary; on the contrary it is the means which the Spirit Himself graciously uses in bringing men to Christ. Every effort, therefore, should be made, with the help of God, to remove objections to this “word of the Cross” and to present it in all its gracious power.
from: J. Gresham Machen, What is Faith (Edinburgh: Banner of Truth, 1991), pp. 143-144 [First Published 1925]