This is what John the Baptist proclaimed:
“One mightier than I is coming after me. I am not worthy to stoop and loosen the thongs of his sandals. I have baptized you with water; he will baptize you with the Holy Spirit.”
It happened in those days that Jesus came from Nazareth of Galilee and was baptized in the Jordan by John. On coming up out of the water he saw the heavens being torn open
and the Spirit, like a dove, descending upon him.
And a voice came from the heavens, “You are my beloved Son; with you I am well pleased.”
See also, Marcellino D’Ambrosio’s article about this feast day.