Well, Christmas is a holiday that celebrates the birth of Jesus Christ, and as such, it is a very important day for many people. However, there are some people who may not celebrate Christmas, or who may celebrate it in a more secular way. Additionally, some people may not celebrate Christmas because they do not believe in Christianity, or because they follow other religions or belief systems. So, in summary, whether or not there is mass on Christmas Day depends on the individual and their personal beliefs and traditions.