A friend tells me that Jesus was probably born in the summer. How do I explain to her the reason the Church celebrates Christmas on December 25?
As we do not know the exact date of Christ’s birth, the date of December 25 for Christmas may have been arbitrary. The Church could have chosen another date on which to celebrate the birth of Christ. One reason December 25 may have been deemed suitable is its proximity to the winter solstice. After that date the days start to become longer, and thus it is at the beginning of a season of light entering the world (cf. John 1:5). The summer solstice—after which the days start to get shorter—falls near June 24, on which the Church celebrates the birth of John the Baptist, who declared of Christ, “He must increase, but I must decrease” (John 3:30).