Why would Mark begin an account of the gospel of Jesus with a description of John the Baptist? Well, when you think about John the Baptizer, you always need to think about Jesus. That was John’s desire and that was John’s ministry—that was his purpose— to point the world to Jesus.

As Mark points out from the very beginning of his account of Jesus, before the Messiah would be revealed in His public ministry, His messenger would come first.
That messenger would prepare the people of Israel for their promised King by declaring the need for repentance. A repentance that spoke of salvation. To receive the King and to enter the Kingdom would require a penitent turning from sin and a believing turning to the Messiah.