I. The yearly observance of the Epiphany is profitable to Christians
It is the right and reasonable duty of true piety, dearly-beloved, on the days which bear witness to the works of Divine mercy, to rejoice with the whole heart and to celebrate with all honour the things which have been wrought for our salvation: for the very law of recurring seasons calls us to such devout observance, and has now brought before us the feast of the Epiphany, consecrated by the Lord's appearance soon after the day on which the Son of God co-eternal with the Father was born of a Virgin.
And herein the providence of God has established a great safeguard to our faith, so that, while the worship of the Saviour's earliest infancy is repeated year by year, the production of true man's nature in Him might be proved by the original verifications themselves. For this it is that justifies the ungodly, this it is that makes sinners saints, to wit the belief in the true Godhead and the true Manhood of the one Jesus Christ, our Lord: the Godhead, whereby being before all ages “in the form of God” He is equal with the Father: the Manhood whereby in the last days He is united to Man in the “form of a slave.”
For the confirmation therefore of this Faith which was to be fore-armed against all errors, it was a wondrous loving provision of the Divine plan that a nation which dwelt in the far-off country of the East and was cunning in the art of reading the stars, should receive the sign of the infant's birth who was to reign over all Israel. For the unwonted splendour of a bright new star appeared to the wise men and filled their mind with such wonder, as they gazed upon its brilliance, that they could not think they ought to neglect what was announced to them with such distinctness.
And, as the event showed, the grace of God was the disposing cause of this wondrous thing: who when the whole of Bethlehem itself was still unaware of Christ's birth, brought it to the knowledge of the nations who would believe, and declared that which human words could not yet explain, through the preaching of the heavens.
Source: Sermons (New Advent)