Then Jesus came from Galilee to the Jordan to be baptised by John. But John tried to deter him, saying, "I need to be baptised by you, and do you come to me?" Jesus replied, "Let it be so now; it is proper for us to do this to fulfil all righteousness." Then John consented.
As soon as Jesus was baptised, he went up out of the water. At that moment heaven was opened, and he saw the Spirit of God descending like a dove and lighting on him. And a voice from heaven said, "This is my Son, whom I love; with him I am well pleased."
I love the account of Jesus's baptism. Remarkably similar in all four Gospels, it's a wonderful example of how the Gospel writers combine the eyewitness accounts of Jesus's life with profound theological truth (Clayboy has a good post giving the more scholarly take on this).
It's an Epiphany reading because it's a moment of revelation - when we see who Jesus really is. In the Gospels it acts as a sneak preview for the reader: as we go through the rest of the story and people keep asking "who is this?", we already know the answer, because God has told us; "this is my Son". For Jesus, it was certainly a moment of understanding about his mission, but it also confirms his relationship with his Father: not just for him, but for us too, as we see, for the first time, Father, Son and Holy Spirit working together.
At the Jordan we see that Jesus really is who he claims to be. The voice of God speaks to us as we worship today. The Father trusts the Son to be the saviour of the world and calls us to trust him too.