“Sin always has a destructive effect, but often that effect isn’t immediately obvious. Over a period of time, however, where sin is indulged, there’ll be a hardening effect on the soul of a genuinely converted Christian.
To differing degrees we’re all familiar with this hardening effect. Perhaps you gradually find yourself less affected by corporate worship in your local church. Or you’ve recently noticed that your appetite for Holy Scripture has diminished. You may be less sensitive to sin, or your confession of sin is less frequent and lacks sorrow.
The ultimate effect from such hardening by sin is that grace, for the Christian is no longer amazing. That’s why we need to stay close to the doctrine of sin – because it helps us see the presence of pride and protects us from those hardening effects. The doctrine of sin was specifically designed for this, and it’s sufficiently potent to put pride to death in our lives by the power of the Holy Spirit.”
C.J. Mahaney, Humility: True Greatness. (Colorado Springs: Multnomah, 2005), 93.