After the feast of Christmas, the Church honors an interesting pair of saints in the calendar. The first two saints during the octave of Christmas are not directly tied to the Nativity of Jesus Christ, but are inserted at this time of the year to recognize their extraordinary example of holiness. The feast of St. Stephen on December 26 is followed by that of St. John the Evangelist on December 27.
Emphasis on the divinity of Christ
First of all, some commentators have pointed out St. John's emphasis on the divinity of Christ in his Gospel as being an apt reason for celebrating him in the Christmas octave.
The St. Andrew Daily Missal makes this point in its description of the feast.
It is God whom we adore at Bethlehem during Christmas time. Thus it was natural that St. John, the chief evangelist of the divinity of Christ, should be found beside the crib, to disclose the greatness of the Infant who reposes therein.
Prince of Virgins
Dom Prosper Gueranger makes a different point in his Liturgical Year, explaining how St. John is honored for his example of virginal love.
Nearest to Jesus' Crib after Stephen, stands John the Apostle and Evangelist. It was only right that the first place should be assigned to him, who so loved his God that he shed his blood in his service...But next to the sacrifice of Blood, the noblest the bravest and which most wins the heart of Him, who is the Spouse of souls, is the sacrifice of Virginity.
Now just as St. Stephen is looked upon as the type of Martyrs, St. John is honored as the Prince of Virgins. Martyrdom won for Stephen the Crown and palm, Virginity merited for John most singular prerogatives which, while they show how dear to God is holy Chastity, put this Disciple among those who by their dignity and influence are above the rest of men.
It is this pure love that gave St. John the strength to stay beside Christ at the foot of the cross, when all the other apostles scattered.
While we ponder the mysteries of Christmas, we are already looking forward to Jesus' supreme act of salvation, his sacrifice on the cross.