Holy days were once a requirement under Israel’s law. Those days had special significance for God’s prophetic purpose on the earth. When the mystery is revealed to Paul special days no longer have a place for the new creature, the Body of Christ (Gal 4:9-11).
“Let no man therefore judge you in meat, or in drink, or in respect of an holyday, or of the new moon, or of the sabbath days” – Col 2:16