God, religion, festivals, etc.

Do you have to believe in God to celebrate Diwali or Ramzan? In any case, I don't believe in God or festivals. But it's a holiday. Will sleep late and laze around. This buying sweets, clothes and stuff seems like a pointless thing to do. At times, at least. Especially when I see the large crowds in places like T.Nagar.
Lately, as Diwali drew nearer, I felt the whole thing had gotten much too materialistic for me. Why must the celebration of good over evil be so messy?