In those days came John the Baptist, preaching in the wilderness of Judea,
All Commentaries on Matthew 3:1 Go To Matthew 3
Theophylact of Ochrid
AD 1107
Not when the Lord was a child and was living in Nazareth, but rather the evangelist makes this simple statement, "at that time, before the present generation."
John was sent by God to reprove the Jews and to persuade them to come to a consciousness of their own sins and so to accept the Christ. For if one is not conscious of his sins, he cannot come to repentance. This is why John was sent.