Midnytes is correct. Mainstream Christian 'Holy' days are very unholy in that they are mostly papist or Roman Catholic in origin. This means they are heathen or pagan in origin.
All Rome did in order gather a following is incorporate all the heathen religions into its own and then call the incorporated heathen festivals religious names in order to make them sound Christian i.e. Christmas which in reality is the Feast of Sol Invictus the feast of the unconquered sun or to us in this modern age a winter solstice celebration.
True Christians can choose any day of the year and make it Holy to the Lord if they so desire but as long as they do not make it binding on their brothers and sisters.