“We make this assertion because this is what the liturgy itself tells us, in the very acts of making us manifest and like to Christ. The manifestation and full meaning of Christ to the world is given in the Christmas cycle of the liturgy, beginning with the feast of the Nativity, the Incarnation itself. This feast was originally kept on January 6th, but probably following the arguments of Sextus Julius Africanus (supposedly relating the records of the Roman censuses to the birth of Christ), the actual birth of Christ was redated to December 25. Gueranger reports that the Holy See ‘obliged all Churches to keep the Nativity on this date [nevertheless] the Sixth of January was not robbed of its glory.’ So important was the date of the feast on the 6th of January, however, that the established feast on that date remained, in both the East and the West. We might say that the historical considerations were subordinated to their anagogical and theological significance, but this would not be quite correct, for the keeping of the Nativity as the actual birth of Christ was already subordinate to two other significations of the feast (so much so, that it gets no mention in the liturgies of the East) is the appearance of the wise men or Magi from the East, the so-called ‘three kings’.”
Laurence Paul Hemming, Worship as a Revelation, p. 164.