[There was a man sent from God, whose name was John.] He came as a witness to testify to the light, so that all might believe through him. (John 1:7)
The first advent was the period of time waiting for the Savior to arrive. The second advent is Jesus’s coming again to reign in power. It wasn’t until this year that the time just before Jesus’s public ministry is also an advent, especially the ministry of John the Baptist, who testified to Jesus, the Light of the world.
And this is the testimony of John, when the Jews sent priests and Levites from Jerusalem to ask him, “Who are you?” He confessed, and did not deny, but confessed, “I am not the Christ.” 21And they asked him, “What then? Are you Elijah?” He said, “I am not.” “Are you the Prophet?” And he answered, “No.” So they said to him, “Who are you? We need to give an answer to those who sent us. What do you say about yourself?” He said, “I am the voice of one crying out in the wilderness, ‘Make straight the way of the Lord,’ as the prophet Isaiah said.”
(Now they had been sent from the Pharisees.) They asked him, “Then why are you baptizing, if you are neither the Christ, nor Elijah, nor the Prophet?” John answered them, “I baptize with water, but among you stands one you do not know, even he who comes after me, the strap of whose sandal I am not worthy to untie.” These things took place in Bethany across the Jordan, where John was baptizing.
The next day he saw Jesus coming toward him, and said, “Behold, the Lamb of God, who takes away the sin of the world! This is he of whom I said, ‘After me comes a man who ranks before me, because he was before me.’ I myself did not know him, but for this purpose I came baptizing with water, that he might be revealed to Israel.” And John bore witness: “I saw the Spirit descend from heaven like a dove, and it remained on him. I myself did not know him, but he who sent me to baptize with water said to me, ‘He on whom you see the Spirit descend and remain, this is he who baptizes with the Holy Spirit.’ And I have seen and have borne witness that this is the Son of God.”
The next day again John was standing with two of his disciples, and he looked at Jesus as he walked by and said, “Behold, the Lamb of God!” The two disciples heard him say this, and they followed Jesus. (John 1:19-36)
And then, for most intents and purposes, John drops out of the story, except, in the gospel of John, to witness onec more to Jesus:
And [John’s disciples] came to John and said to him, “Rabbi, he who was with you across the Jordan, to whom you bore witness–look, he is baptizing, and all are going to him.” John answered, “A person cannot receive even one thing unless it is given him from heaven. You yourselves bear me witness, that I said, ‘I am not the Christ, but I have been sent before him.’ The one who has the bride is the bridegroom. The friend of the bridegroom, who stands and hears him, rejoices greatly at the bridegroom’s voice. Therefore this joy of mine is now complete. He must increase, but I must decrease.” (John 3:26-30)
John the Baptist’s taglines: “He confessed, and did not deny, but confessed, ‘I am not the Christ.'” and “He must increase, but I must decrease.”