"Today the Church celebrates the Solemnity of the Nativity of Saint John the Baptist, and on 29 August, we will celebrate the memorial of his martyrdom. There is no other saint for whom the Church celebrates both of these moments. Generally, it celebrates only their “birth into heaven”, with the exception, of course, of Jesus, the Son of God (25 December – his birth; and Good Friday – his death) and the Virgin Mary (8 September – her birth; and 15 August – her Assumption into heaven).
Jesus himself said, “Amen, I say to you, among those both of women there has been none greater than John the Baptist” (Mt. 11:11). He was the last of the great prophets of Israel, the first to testify to Jesus, who initiated a baptism for the forgiveness of sins and, in this context, baptized Jesus; he was a martyr who died defending the Judaic law.
As early as the 4th century, we find a liturgical commemoration for Saint John the Baptist celebrated on a variety of dates. The date of 24 June was established based on Lk 1:36a where speaking of Elizabeth it says, “this is the sixth month for her who was called barren”, therefore, six months before Christmas. Since the 6th century, this Feast also had a vigil."