It just occurred to me that the feast of the Holy Innocents is on December 28, three days after Christmas; but Epiphany, when the Magi arrived is always in January. But the Holy Innocents were killed after the Magi left. Why does the Church commemorate the martyrdom of the Holy Innocents before it celebrates the arrival of the Magi?
The arrangement of the Church’s liturgical calendar is not always intended to be in chronological order. Sometimes feast days are arranged by theological significance.
In this case, there are a slew of feast days right after Christmas that emphasize the fact that the events surrounding Christmas were an anticipation of Christ’s eventual passion, death, and resurrection. On December 26 is the feast of St. Stephen Protomartyr, the first Christian martyr after the establishment of the Church. December 27 is the feast of St. John the Evangelist, the Beloved Disciple who stood at the foot of the Cross and received the Blessed Mother from Christ to be his own Mother. December 29 is the feast of St. Thomas Becket, bishop and martyr. In the midst of this is December 28, the feast of the Holy Innocents, the first martyrs after the birth of Christ.
In short, the Church’s placement of a slew of martyrs’ feast days right after Christmas is intended to remind Catholics that Christ was, as Bishop Fulton Sheen once pointed out, the only man born to die. Christmas is important because it made possible Easter.