John describes himself as a herald, who announces the arrival of someone else, the Mightier One. Compared to him, John is no more than a slave. That Jesus is above John is also apparent from their way of baptizing: John baptizes with water (washing clean, washing away of sins), while Jesus will baptize with the Holy Spirit (giving a new life, in agreement with the holy God).
7 And he preached, saying, “After me comes he who is mightier than I, the strap of whose sandals I am not worthy to stoop down and untie.