Imagine going to a talk and hearing the keynote speaker introduced by someone who knew the content of the talk but not the identity of the speaker. This was John. He proclaimed the coming of the Messiah without knowing exactly who the Messiah was. Listen and learn his call to repentance.
from Matthew 3:1-12
John the Baptist appeared, preaching in the desert of Judea
and saying, "Repent, for the kingdom of heaven is at hand!"
It was of him that the prophet Isaiah had spoken when he said:
A voice of one crying out in the desert,
Prepare the way of the Lord,
make straight his paths.
John wore clothing made of camel's hair
and had a leather belt around his waist.
His food was locusts and wild honey.
At that time Jerusalem, all Judea,
and the whole region around the Jordan
were going out to him
and were being baptized by him in the Jordan River
as they acknowledged their sins.
Read the full scripture passage: https://bible.usccb.org/bible/readings/120422.cfm