From the Second Sermon on the Epiphany by St. Leo the Great:
Dearly beloved brethren, rejoice in the Lord; again I say, rejoice. But a few days are past since the solemnity of Christ's Birth, and now the glorious light of His Manifestation is breaking upon us. On that day the Virgin brought Him forth, and on this the world knew Him. The Word made Flesh was pleased to reveal Himself by degrees to those for whom He had come. When Jesus was born He was manifested indeed to the believing, but hidden from His enemies. Already indeed the heavens declared the glory of God, and their sound went out into all lands, when the Herald Angels appeared to tell to the shepherds the glad tidings of a Saviour's Birth; and now the guiding star leadeth the wise men to worship Him, that from the rising of the sun to the going down thereof, the Birth of the true King may be known abroad; that through those wise men the kingdoms of the east might learn the great truth, and the Roman empire remain no more in darkness.
The very cruelty of Herod, when he strove to crush at His birth this King Whom he alone feared, was made a blind means to carry out this dispensation of mercy. While the tyrant with horrid guilt sought to slay the little Child he did not know, amid an indiscriminate slaughter of innocents, his infamous act served to spread wider abroad the heaven-told news of the Birth of the Lord. Thus were these glad tidings loudly proclaimed, both by the novelty of their story, and the iniquity of their enemies. Then was the Saviour borne into Egypt, that nation, of a long time hardened in idolatry, might by the mysterious virtue which went out of Him, even when His presence was unknown, be prepared for the saving light so soon to dawn on them, and might receive the Truth as a wanderer even before they had banished falsehood.
Dearly beloved brethren, we recognise in the wise men who came to worship Christ, the first-fruits of that dispensation to the Gentiles wherein we also are called and enlightened. Let us then keep this Feast with grateful hearts, in thanksgiving for our blessed hope, whereof it doth commemorate the dawn. From that worship paid to the new-born Christ is to be dated the entry of us Gentiles upon our heirship of God and co-heirship with Christ. Since that joyful day the Scriptures which testify of Christ have lain open for us as well as for the Jews. Yea, their blindness rejected that Truth, Which, since that day, hath shed Its bright beams upon all nations. Let all observance, then, be paid to this most sacred day, whereon the Author of our salvation was made manifest, and as the wise men fell down and worshipped Him in the manger, so let us fall down and worship Him enthroned Almighty in heaven. As they also opened their treasures and presented unto Him mystic and symbolic gifts, so let us strive to open our hearts to Him, and offer Him from thence some worthy offering.