Up until this section, there hasn’t been a lot of information about people who opposed Jesus, or even those who ignore him. Now we get the impression that the majority of “this generation” are not on board with Jesus. Of course, we know that and see the same thing today.
Usually when Jesus tells a parable, he is giving us a glimpse into the way the Kingdom works. This time, he is showing more about the people than the Kingdom.
It’s difficult to say exactly what this parable is about, but essentially Jesus is saying “this generation” is spoiled and confused. It may be that they cannot get John to dance and they cannot get Jesus to mourn. Or it may be that John is saying, “Let’s play mourning”, while Jesus is offering the game of “wedding/dancing”, and nothing makes them happy. Either way, the message is really the same.
Craig Keener says it is a “heads I win, tails you lose” situation. They complain about John about one thing. They complain about Jesus for the opposite thing. Some people just like to complain. Isn’t that the truth.
At any rate, real wisdom shows up as good results. The proof is in the pudding. Jesus and John show true wisdom. The people are foolish to ignore them.