Learning how to play guitar comes with its share of difficulties. It can be quite painful at first, until you develop calluses on your fingers. Calluses develop slowly over time, making your fingers less sensitive to the harshness of the strings. Similarly, calluses also fade slowly over time. It might take a few months without playing for a guitarist to completely lose her calluses. What is true for the fingers of a guitarist is also true for the human heart. The heart can easily grow callous over time, losing its sensitivity to the Lord. In the same way, a hardened heart takes time to soften, becoming more sensitive to the Spirit through discipline and development. Christians must remain sensitive to the Spirit’s voice, not enabling callousness to grow and take root in our hearts.