It would be no mistake to call [Christmas] the chief and mother of all holy days. Had Christ not been born of the flesh, he would not have been baptized, which is the theophany or manifestation. Nor would he have been crucified, which is the [Passover]. Nor would he have sent down the Spirit, which is Pentecost. Therefore, just as different rivers arise from a single source, these other feasts [Easter, the Ascension, Pentecost] have their beginnings in the birth of Christ.
—John Chrysostom, On the Incomprehensible Nature of God