This lesson teaches us that nothing is impossible in this world for hard working and wise people.
While making a thing, people use traditional material and follow traditional method. But sometimes we have to follow the method which is against traditional method. People did not succeed in making rope of ash when they used the traditional method. So, in the end, Kalidasa turned the rope into ash using the method against tradition. So when the ash cannot be turned into a rope, the rope can be converted into ash.