The festival without which there would be no festivals

Ascension Day... "that festival which confirms the grace of all the festivals together, without which the profitableness of every festival would have perished. For unless the Saviour had ascended into heaven, his nativity would have come to nothing ... and his passion would have borne no fruit for us, and his most holy resurrection would have been useless."

 Attributed to St Augustine - bonus points to anyone who has a citation

HT: Philip Robertson on The Face Book