The niceness means three different things.You must be friendly and helpful to each other. Secondly you must be good to yourself. It means that it is good to develop yourself by studying, exercising sports and writing letters, for example, and other good things. Thirdly you must be nice towards nature and animals. Kindness and peace are very important things to Santa Claus!
Santa Claus hopes that you will be kind and considerate in the future. He wants you to continue your good hobbies, too. And now, you are ready to visit my homeland and write your Christmas letters