Awake, O man, and recognize the dignity of thy nature. Recollect thou wast made in the image of GOD, which although it was corrupted in Adam, was yet re-fashioned in Christ. Use visible creatures as they should be used, as thou usest earth, sea, sky, air, springs, and rivers: and whatever in them is fair and wondrous, ascribe to the praise and glory of the Maker. Be not subject to that light wherein birds and serpents, beasts and cattle, flies and worms delight. Confine the material light to your bodily senses, and with all your mental powers embrace that “true light which lighteth every man that cometh into this world,” and of which the prophet says, “Come unto Him and be enlightened, and your faces shall not blush.” For if we “are a temple of GOD, and the Spirit of GOD dwelleth in” us, what every one of the faithful has in his own heart is more than what he wonders at in heaven. And so, dearly beloved, we do not bid or advise you to despise GOD’s works or to think there is anything opposed to your Faith in what the good GOD has made good, but to use every kind of creature and the whole furniture of this world reasonably and moderately: for as the Apostle says, “the things which are seen are temporal: but the things which are not seen are eternal.” Hence because we are born for the present and reborn for the future, let us not give ourselves up to temporal goods, but to eternal: and in order that we may behold our hope nearer, let us think on what the Divine Grace has bestowed on our nature on the very occasion when we celebrate the mystery of the LORD ’s birthday. Let us hear the Apostle, saying: “for ye are dead, and your life is hid with Christ in GOD. But when CHRIST, who is your life, shall appear, then shall ye also appear with Him in glory:” who lives and reigns with the Father and the Holy Ghost for ever and ever. Amen.
Leo the Great, On the Feast of the Nativity, VII (Sermon 27)