John the Baptist preached a message of repentance. He called his hearers to turn from their sin and to hope in the One who was coming after him, the One whose sandals he was not worthy to carry. John was that voice of one crying in the wilderness, written about in Isaiah, who cried out, “Prepare the way of the Lord; make his paths straight” (Matthew 3:3 || Isaiah 40:3). John was sent, sent by God to prepare the way of the Lord, for the Lord was indeed coming.
The Apostles, too, preached a message of repentance for the forgiveness of sins. So Jesus, after His resurrection and before ascending into heaven, says to his disciples, Thus it is written, and thus it was necessary for the Christ to suffer and to rise from the dead the third day, and that repentance and remission of sins should be preached in His name to all nations, beginning at Jerusalem (Luke 24:46-47).