MARK 1.1-3: The beginning of the gospel of Jesus Christ, the Son of God. (2) As it is written in Isaiah the prophet, “Behold, I send my messenger before your face, who will prepare your way, (3) the voice of one crying in the wilderness: ‘Prepare the way of the Lord, make his paths straight.'” (ESV)
The Gospels of Matthew, Mark, and Luke are referred to as the Synoptic Gospels because they are written from practically the same vantage point. “Synoptic” can be understood as meaning “viewed together”. Matthew and Luke include their own unique details of the birth of Jesus. Matthew includes the account of the evil actions of Herod and Jesus’ parents taking Him to Egypt until the death of Herod, as well as the visit of the Magi.
Luke gives details about the angelic revelation of the birth of Jesus to the shepherds, and the dedication of Jesus at the Temple. And Luke also provides much information about John the Baptist and how he relates to Jesus, and how God revealed that John would be the prophet and forerunner of Jesus, just prior to Jesus beginning His earthly, public ministry.
And it is with this backdrop that the Gospel of Mark begins with the ministry of John the Baptist as the forerunner and messenger of Jesus. Mark refers to the prophecy of Isaiah as the biblical foundation for the ministry of John the Baptist and he also quotes from Malachi 3.1 so as to connect both of these prophecies into the one person of John the Baptist.
And so the beginning of the Good News of Jesus Christ, who was and is the Son of God, has its beginning with the ministry of the messenger, who will announce the coming of the Messiah who will be the King who sits and reigns on the throne of King David. Likewise, the Messiah will reign according to the will of God the Father. And as such, the King will have an advance messenger, warning the people to get ready.
As we will see from the preaching of John, he spoke warnings to the people, both great and small, of the coming judgment of God upon unrepentant sinners.