‘And when the messengers of John were departed, he began to say to the crowds concerning John, “What did you go out into the wilderness to behold? A reed shaken with the wind?” '
Jesus now turned to challenge the crowds. He did not want them to see John as failing. Indeed the problem lay not with John and his honest doubts, but with those who failed to follow the counsel or purpose of God (Luke 7:30).
So they should now recognise that they had gone out to John in the wilderness, not because he bowed to the winds of the Scribes and Pharisees and of Herod, and to the winds of change, but because he came with a powerful, firm and consistent message. (Anyone less like a reed bending before the wind than John the Baptiser it is difficult to imagine).
The idea here may be taken from 1 Kings 14:15 where a reed in the water, shaken in the wind, is illustrative of those who are rejected by God because of failure.