The Gospels all introduce John the Baptist’s ministry by quoting Isaiah 40.3 (see Matt. 3.3; Luke 3.4; John 1.23). John was called “My messenger” (Mark 1.2), the divinely promised messenger, sent to prepare the way for the Messiah. In ancient times, a king’s envoys would travel ahead of him, making sure the roads were safe and fit for him to travel on, as well as announcing his arrival.
As the last Old Testament prophet and the divinely ordained forerunner of the Messiah, John was the culmination of Old Testament history and prophecy (Luke 16.16) as well as the beginning of the historical record of the gospel of Jesus Christ. Not surprisingly, Jesus designated John as the greatest man who had lived until his time (Matt. 11.11). John’s baptism, being the distinctive mark of his ministry (Mark 1.4), differed from the ritual Jewish washings in that it was a one-time act. The Jews performed a similar one-time washing of Gentile proselytes, symbolizing their embracing of the true faith. That Jews would participate in such a rite was a startling admission that they needed to come to God through repentance and faith just like Gentiles.