The Night of the Festival-Advait

This is the shortest short story I have ever read.
It starts off by describing the scene and then progressed to what was happening in the home of Hajji Guma. Hajji Guma is wondering how to explain to his son that he had planned his marriage already. He seems nervous and almost worried about what would happen if his son, Munir would refuse. Then, he reassured himself by remembering about how Hajji Abd Allah was happy by this choice as well. (Hajji Abd Allah is Hajji Guma's brother.) If Munir marries Hajji Abd Allah's daughter, then Hajji Guma's daughter would also be married. After all this thinking, Hajji Guma gets a telegram from Munir saying that he is going to be married to the head of the company. I think that Hajji Guma takes the news pretty well and is pretty understanding. That surprised me. I thought he would take off and make his son come home and marry someone else instead. Instead he said that Munir was excused because he did not know what the family had been planning. Munir also had an excuse for not inviting the family to the wedding because the family did not have enough money to go to the wedding. I do not understand however, why Khadija wants to send him an express letter and not a telegram of congratulations. I think that this is because she is she doesn't want the letter to be sent and she would not be able to stop it if the telegram, but she would be able to stop the express letter. When done writing the letter, Khadija goes out with Nafusa to drop the letter in the mail box, but rips it up and the two girls toss the paper in the river. I think that this is done because Munir would come back home to see why his family did not respond and would stay and not marry someone else. I'm not sure though......why did they throw the letter in to the river?