St. Gregory the Theologian, Oration 38, Section 4:
This is our festival, this is the feast we celebrate today, in which God comes to live with human beings, that we may journey toward God, or return — for to speak thus is more exact — that laying aside the old human being we may be clothed with the new, and that as in Adam we have died so we may live in Christ, born with Christ and crucified with him, buried with him and rising with him. For it is necessary for me to undergo the good turnaround, and as painful things came from more pleasant things, so out of painful things more pleasant things must return. “For where sin abounded, grace superabounded,” and if the taste [of forbidden fruit] condemned, how much more does the Passion of Christ justify? Therefore we celebrate the feast not like a pagan festival but in a godly manner, not in a worldly way but in a manner above the world. We celebrate not our own concerns but the one who is ours, or rather what concerns our Master, things pertaining not to sickness but to healing, not to the first molding but to the remolding.