Madhav engraved on a stone when Raghu saved him because he believed that good deeds should be remembered forever. Madhav explained that when Raghu slapped him, he wrote it on the sand because negative experiences should not be held onto for long. Just like sand, they can easily be wiped away. However, when Raghu saved his life, Madhav felt it was important to remember this act of kindness for the rest of his life. He wanted to keep the good memory like a message engraved on a stone, which symbolizes permanence and appreciation for someone’s positive actions. This teaches us that good deeds should be cherished and never forgotten.