The Lord hath called me by my name from the womb of my mother, and He hath made my mouth like a sharp sword; in the shadow of His hand He hath protected me, and hath made me as a chosen arrow.
Today is a first class (solemn) feast day, and one of only three feast days in the whole ecclesiastical calender which celebrate natural birthdays. The other two are the births of Christ (Dec. 25) and Mary (Sept. 8), who together with St. John are the only three human beings ever to be born without the stain of original sin. Christ and our Lady, of course, were conceived without sin, while the Baptist was sanctified in the womb by the presence of our Lord and Lady at the Visitation.
St. John said of Christ, that "He must increase, but I must decrease" (Jn. 3:30). Appropriately, then, our Lord's birthday comes at the Winter Solstice when the days begin to increase, while St. John's comes at the Summer Solstice when the days begin to decrease.