The mission of St. John the Baptist is to call us to repent of our sins so that we will be ready to welcome Christ.
This is what St. John said, as recorded in the New Testament:
Repent, for the Kingdom of heaven is at hand. (Matthew 3:2-3)
Brood of vipers, who warned you to fly from the retribution that is coming? But if you are repentant, produce the appropriate fruit, and do not presume to tell yourselves, ‘We have Abraham for our father,’ because, I tell you, God can raise children for Abraham from these stones. Even now the axe is laid to the roots of the trees, so that any tree which fails to produce good fruit will be cut down and thrown into the fire. (Matthew 3:8-10/Luke 3:7-9)
To King Herod: It is against the law for you to have your brother’s wife. (Matthew 14:4, Luke 6:18)
When all the people asked him, What must we do then? He answered, ‘If anyone has two tunics he must share with the man who has none, and the one with something to eat must do the same.’
There were tax collectors too who came for baptism, and these said to him, ‘Master, what must we do?’ He said to them, ‘Exact no more than your rate.’
Some soldiers asked him in their turn, ‘What about us? What must we do?’ He said to them, ‘No intimidation! No extortion! Be content with your pay!’ (Luke 3:10-14)
I baptize you in water for repentance, but the one who follows me is more powerful than I am, and I am not fit to carry his sandals; he will baptize you with the Holy Spirit and fire. His winnowing fan is in his hand; he will clear his threshing-floor and gather his wheat into the barn; but the chaff he will burn in a fire that will never go out. (Matthew 3:11-12/Luke 3:16-17)
Someone is following me, someone who is more powerful than I am, and I am not fit bo kneel down and undo the strap of his sandals. I have baptized you with water, but he will baptize you with the Holy Spirit. (Mark 1:7-8)
‘I am not the Christ.’ Are you Elijah? ‘I am not.’ Are you the prophet? ‘No.’ Who are you? ‘I am, as Isaiah prophesied: a voice that cries in the wilderness: Make a straight way for the Lord.’ Why are you baptizing? ‘I baptize with water, but there stands among you—unknown to you—the one who is coming after me, and I am not fit to undo his sandal strap.’ (John 1:21-28)
Pointing to Christ: Look, there is the Lamb of God. (John 1:36)
To Christ: It is I who need baptism from you, and yet you come to me? (Matthew 3:14)
Look, there is the Lamb of God that takes away the sin of the world. This is the one I spoke of when I said: A man is coming after me who ranks before me because he existed before me. I did not know him myself, and yet it was to reveal him to Israel that I came baptizing with water.
I saw the Spirit coming down on him from heaven like a dove and resting on him. I did not know him myself, but he who sent me to baptize with water had said to me, ‘the man on whom you see the Spirit come down and rest is the one who is going to baptize with the Holy Spirit.’ Yes I have seen and I am the witness that he is the Chosen One of God. (John 1:29-34)
A man can lay claim only to what is given him from heaven. You yourselves can bear me out. I said: I myself am not the Christ; I am the one who has been sent in front of him.
The bride is only for the bridegroom; and yet the bridegroom’s friend, who stands there and listens, is glad when he hears the bridegroom’s voice. This same joy I feel, and now it is complete.
He must grow greater; I must grow smaller. He who come from above is above all others; he who is born of the earth is earthly himself and speaks in an earthly way. He who comes from heaven bears witness to the things he has seen and heard, even if his testimony is not accepted. All who do accept his testimony are attesting the truthfulness of God, since he who God has sent speaks God’s own words: God gives him the Spirit without reserve.
The Father loves the Son and has entrusted everything to him. Anyone who believes in the Son has eternal life, but anyone who refuses to believe in the Son will never see life: the anger of God stays on him. (John 3:27-36)
St. Luke about John the Baptist: ‘As well as this, there were many other things he said to exhort the people and to announce the Good News to them.’