He must increase, I must decrease
Today is exactly six months before Christmas, and for this reason we keep the birthday of St John the Baptist.
At one time the nativity of the Baptist was marked by three Masses, just like the nativity of Our Lord. John's birth at the brightest time of the year, just as the nights slowly start to lengthen again, reminds us of his insistence that he should grow less, while the Lord must grow greater. Our Lord's birth at the darkest time of the year (in the northern hemisphere) shows how He is the Light come to illuminate our darkness.
St Philip and the first Oratorians had care of the church of San Giovanni dei Fiorentini - the Florentine national church, dedicated to St John the Baptist.