The postman laughed heartily when he read the address on the letter addressed to God in the story "A Letter to God". The address was "To God, in the clouds". This is a humorous situation because the postman knows that God does not have a physical address in the clouds, and he understands that the letter's sender is a simple farmer who is not aware of this fact.

Explanation:

The story "A Letter to God" is about a poor farmer named Lencho who writes a letter to God requesting for money to help him and his family survive the harsh weather conditions. Lencho believes that God will send him the money, and he is confident that his letter will reach God. He writes the letter and addresses it "To God, in the clouds" and gives it to the postman to deliver.

The postman is amused by the address on the letter because he knows that God does not have a physical address in the clouds. The postman understands that Lencho is a simple farmer who is not aware of this fact, and he finds the situation humorous. The postman laughs heartily, and this shows his amusement at the situation.

The humor in this situation is that Lencho is a simple and innocent man who believes that God will send him the money he needs. He writes a letter to God and addresses it in a way that shows his lack of knowledge about how the postal system works. The postman, who is familiar with the postal system, finds this amusing and laughs heartily at the situation.

In conclusion, the postman laughs heartily when he reads the address on the letter addressed to God because he understands that the sender is a simple farmer who is not aware that God does not have a physical address in the clouds. This situation is humorous because it shows the innocence and naivety of the sender, and the familiarity of the postman with the postal system.

The Postman laughed heartily because of the letter written by lencho as he had never seen such a great faith in God before and postman also never had seen someone sending a letter to God... he never saw the address written "to God" in his whole career ...