Catholic feast days are traditionally set on the anniversary of a saint’s death. In Catholic theology, this date is celebrated as their dies natalis or "heavenly birthday," marking the moment they entered eternal life rather than their earthly birth.
John the Baptist is an exception...we the day of his birth not as a Feast Day, but rather a Solemnity.....the highest form of Catholic feast day.
John's birth is celebrated because he was "set apart from the womb" as the unique precursor or forerunner, chosen to prepare the way for Jesus. St. John the Baptist is one of only three people in history — after Jesus and Mary — whose birthday is celebrated in the Church’s liturgy.
The Nativity of St. John the Baptist on June 24 falls exactly six months before the solemnity of the Nativity of Our Lord, and it is sometimes known as “Summer Christmas.”
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