A student of Islamic knowledge and his advice

The scholar Ibn al-Jawzi رَحْمَةُ الـلّٰـهِ عَلَيْه relates:

A young student had a slate upon which he would write his lessons down with ink. He began washing it to clear away his previous lesson, but the ink was not going anywhere. He then took some rope, drenched it in water and covered it with earth, which eventually solidified. He then used this along with water to scrub away the ink.

A person nearby watched the boy doing this and asked, “Why are you scrubbing your slate with this rope?” The student replied by saying the ink had set firmly into the slate, and he was using the rope to help wash it away. “Can ink be removed using a rope?”, the person quizzed.  

The young student was intelligent and responded immediately, “Yes! Think about it; We tie a rope to a bucket and lower it into this well for water. After a while, the rope leaves a groove on the side of it (if rope can cut into stone, why would it not be able to scrub away this ink?).”

The person said, “But the rope will only leave a groove in the rock after a long time has passed.”

“Not at all”, the student exclaimed, “A groove is formed by pulling the rope. If the rope is not pulled, a groove will not form in the rock even if centuries pass by.” The student then began offering the person advice, and said, “I have given you a subtle hint. If you think this example over, the darkness of your heart will also be washed away.”

“Wait, is there darkness in my heart?”, the person asked.