St. Leo the Great on Nativity

5th century AD. From his Sermon 21, from Day by Day with the Early Church Fathers:

Our dearly beloved Savior was born today. Let us be glad! For there isn't a proper place for sadness when we celebrate the birthday of...Life. For this Life destroys our fear of death and brings us the joy of promised eternity. Everyone can share in this happiness. There is the same amount of joy for everyone. For our Lord destroys sin and death and finds everyone guilty, but has come to free us all. Let saints rejoice at their nearness to victory. Let sinners be glad that they are invited to be pardoned.... Let us, then, dearly beloved, give thanks to God the Father, through His Son, in the Holy Spirit. Because of "His great mercy, wherewith He has loved us," He had pity on us. And "when we were dead in sins, [He] has quickened us together in Christ," so that we can be new creations in Him. So then, let us put off the old self with its deeds and, sharing in Christ's birth, let us defy fleshly works. Christians, acknowledge your dignity. As you become a partner in God's nature, refuse to return to the old, wicked behavior. Remember the Head and the body [of] which you are members. Remember that you were rescued from the power of darkness and brought out into God's light and kingdom.