From the Treasury of Daily Prayer:

In contrast to the Nativity of St. John the Baptist (observed on June 24), this festival commemorates his beheading by the tetrarch Herod Antipas (Mark 6:14-29). From the perspective of the world, it was an ignominious end to John the Baptist’s life. Yet it was in fact a noble participation in the cross of Christ, which was John’s greatest glory of all. Christ Himself said that there had arisen none greater than John the Baptist (Matthew 11:11). He was the last of the Old Testament prophets and also the herald of the New Testament. As the forerunner of Christ, John fulfilled the prophecy that the great prophet Elijah would return before the great and terrible Day of the Lord (Malachi 4:5; Matthew 17:10-13). By his preaching and Baptism of repentance, John turned “the hearts of fathers to their children and the hearts of children to their fathers” (Malachi 4:6). And in the footsteps of the prophets who had gone before him–in anticipation of the Christ whose way he prepared–this servant of the Lord manifested the cross by the witness of his death.