Celebrations of new moons and festivals were often associated with worship of gods. There were the gods of the harvest, the gods of the river, the gods of the New Year and many others. The celebration of Christmas was originally a pagan holiday celebrating the solstice. So why did Paul write, “So let no one judge you … regarding a festival, or a new moon or Sabbaths”?
Because God is not troubled by human traditions. As Paul points out, our celebrations are only shadows. A police officer doesn’t give you a ticket because your shadow went out into the traffic. If a car runs over your shadow both you and your shadow survive. Shadows are only silhouettes of our bodies. Our celebrations are silhouettes of what we believe.
Paul is not advocating celebrating other gods or saying to join in their celebrations is acceptable. But if you have converted a previous celebration into that which honors God, don’t let people make you feel guilty about that (Colossians 2:16-19).