It's religious because it celebrates the day that Christians believe that Jesus was born.
It
commemorates the day Jesus was born, but wasn't the day. It's date had to do with the Church, at the time, trying to ease Pagan converts into Christianity and to shift focus away from the Winter Solstice celebrations. Over time it and its traditions have become controversial to Christians and non-Christians alike (Perhaps not even over time. Since its creation many saw it as a false holiday). It is a conglomerate of traditions and beliefs that have become the beautiful ball of happiness that we know today. It is the perfect example of what can happen when, over time, people decide to embrace culture instead of rejecting anything unfamiliar. It is irreligious, but filled with Faith; Christmas is a holiday for anyone who can understand togetherness, kindness, and Love.