‘On this the Day which the Lord hath made,’ says St Gregory of Nyssa, ‘darkness decreases, light increases, and Night is driven back again. No, brethren, it is not by chance, nor by any created will, that this natural change begins on the day when he shows himself in the brightness of his coming, which is the spiritual Life of the world. It is Nature revealing, under this symbol, a secret to them whose eye is quick enough to see it; to them, I mean, who are able to appreciate this circumstance of our Saviour’s coming. Nature seems to me to say: Know, O Man! that under the things which I show thee Mysteries lie concealed. Hast thou not seen the night, that had grown so long, suddenly checked? Learn hence, that the black night of Sin, which had reached its height by the accumulation of every guilty device, is this day stopped in its course. Yes, from this day forward its duration shall be shortened, until at length there shall be naught but Light. Look, I pray thee, on the Sun; and see how his rays are stronger, and his position higher in the heavens: learn from that how the other Light, the Light of the Gospel, is now shedding itself over the whole earth.’ [Homily On the Nativity.]
"Let us, my Brethren, rejoice,’ cries out St Augustine: ‘this day is sacred, not because of the visible sun, but because of the Birth of him who is the invisible Creator of the sun. ... He chose this day whereon to be born, as he chose the Mother of whom to be born, and he made both the day and the Mother. The day he chose was that on which the light begins to increase, and it typifies the work of Christ, who renews our interior man day by day. For the eternal Creator having willed to be born in time, his Birthday would necessarily be in harmony with the rest of his creation.’
The same holy Father, in another sermon for the same Feast, gives us the interpretation of a mysterious expression of St John Baptist, which admirably confirms the tradition of the Church. The great Precursor said on one occasion, when speaking of Christ: He must increase, but I must decrease [St John iii 30]. These prophetic words signify, in their literal sense, that the Baptist’s mission was at its close, because Jesus was entering upon his. But they convey, as St Augustine assures us, a second meaning: ‘John came into this world at the season of the year when the length of the day decreases; Jesus was born in the season when the length of the day increases.’ [Sermon In Natali Domini, xi]. Thus, there is mystery both in the rising of that glorious Star, the Baptist, at the summer solstice: and in the rising of our Divine Sun in the dark season of winter.
[...] There have been men who dared to scoff at Christianity as a superstition, because they discovered that the ancient Pagans used to keep a feast of the sun on the winter solstice! In their shallow erudition they concluded that a Religion could not be divinely instituted, which had certain rites or customs originating in an analogy to certain phenomena of this world: in other words, these writers denied what Revelation asserts, namely, that God only created this world for the sake of his Christ and his Church. The very facts which these enemies of our holy Religion brought forward as objections to the true Faith are, to us Catholics, additional proof of its being worthy of our most devoted love."
