The baptism of Jesus
Jesus' public life begins with his baptism by John in the Jordan. John preaches "a baptism of repentance for the forgiveness of sins". A crowd of sinners - tax collectors and soldiers, Pharisees and Sadducees, and prostitutes - come to be baptized by him. "Then Jesus appears." the Baptist hesitates, but Jesus insists and receives baptism. Then the Holy Spirit, in the form of a dove, comes upon Jesus and a voice from heaven proclaims, "This is my beloved Son." This is the manifestation ("Epiphany") of Jesus as Messiah of Israel and Son of God.
Source: Catechism of the Catholic Church (Vatican.va)