Forecast ... Partly Cloudy
Sandwiched inbetween parables about the kingdom of God, possessions, wealth, and faith is a strong warning about God's judgement. My feeling is that folks might have been falling asleep in the heat of the day and Jesus wanted to be sure they were paying attention. Jesus' overall message is about a loving God so this touch of John the Baptist might just be for effect or as a reminder that it is still important to repent (aka get with the program).