-- Is 49:1-6
St. John the Baptist is the Lord's immediate precursor or forerunner, sent to prepare his way. "Prophet of the Most High", John surpasses all the prophets, of whom he is the last. He inaugurates the Gospel, already from his mother's womb welcomes the coming of Christ, and rejoices in being "the friend of the bridegroom", whom he points out as "the Lamb of God, who takes away the sin of the world". Going before Jesus "in the spirit and power of Elijah", John bears witness to Christ in his preaching, by his Baptism of conversion, and through his martyrdom.
-- CCC 523
Art: Domenico Ghirlandaio, Birth of St. John the Baptist