The cross used to denote punishment but it has now become a focus of glory. It was formerly a symbol of condemnation but it is now seen as a principle of salvation. For it has now become the source of innumerable blessings: it has delivered us from error, enlightened our darkness, and reconciled us to God; we had become God's enemies and were foreigners afar off, and it has given us his friendship and brought us close to him. For us it has become the destruction of enmity, the token of peace, the treasury of a thousand blessings.
Thanks to the cross we are no longer wandering in the wilderness, because we know the right road; we are no longer outside the royal palace, because we have found the way in; we are not afraid of the devil's fiery darts, because we have discovered the fountain. Thanks to the cross we are no longer in a state of widowhood, for we are reunited to the Bridegroom; we are not afraid of the wolf, because we have the good shepherd: "I am the good shepherd," he said. Thanks to the cross we dread no usurper, since we are sitting beside the King.
That is why we keep festival as we celebrate the memory of the cross. St. Paul himself invites us to this festival in honor of the cross: "Let us celebrate the feast not with the old leaven, that of corruption and wickedness, but with the unleavened bread of sincerity and truth." And he tells us why, saying, "Christ, our Passover, has been sacrificed."
Now do you see why he appoints a festival in honor of the cross? It is because Christ was immolated on the cross. And where he was sacrificed, there is found abolition of sins and reconciliation with the Lord; and there, too, festivity and happiness are found: "Christ, our Passover, has been sacrificed."
Where was he sacrificed? On a gibbet. The altar of this sacrifice is a new one because the sacrifice himself is new and extraordinary. For he is at one and the same time both victim and priest; victim according to the flesh and priest according to the spirit.
This sacrifice was offered outside the camp to teach us that it is a universal sacrifice, for the offering was made for the whole world; and to teach us that it effected a general purification and not just that of the Jews. God commanded the Jews to leave the rest of the world and to offer their prayers and sacrifices in one particular place; because all the rest of the world was soiled by the smoke and smell of all the impurities of pagan sacrifices. But for us, since Christ has now come and purified the whole world, every place has become an oratory.
(St. John Chrysostom, Homily 1 on the Cross and the Thief 1: PG 49, 399-401; as cited in J. Robert Wright, Readings for the Daily Office from the Early Church, 163-164)