“The holy canons dictate that Christians should spend the eves of feast days in prayer and with reverence in preparation for participation or attendance at the Divine Liturgy. If all Orthodox Christians are called to this, then this pertains all the more to those who take an active part in the church services itself.
Their participation in diversions on the eve of a feast day is especially sinful. In view of the above, those who attend a dance or similar form of entertainment and diversion may not participate in the choir the next day, may not serve in the altar, enter the altar or stand on the cliros.”
St. John the Wonderworker of Shanghai and San Francisco, Ukase concerning the inadmissibility of engaging in entertainments on the eves of feast days.
Quoted from Man of God: Saint John of Shanghai & San Francisco.