Jesus concludes this section of Gospel with a searching rebuke to the Jews of the day. He likens the nation of Israel to a demon possessed man from whom the demon leaves for a while. However, not finding any other mischief to perform, the demon returns to the man and finds him put in order and clean. So the demon finds seven spirits more wicked than himself and together they enter the man, so that his final state is worse than the first.
Israel had for much of its history rebelled against God. They had received a gracious blessing from God only 400 years before in being allowed to return to their own land and rebuild the temple. Yet they returned to the very sins which had brought about their exile - being like a man possessed by an evil spirit. Through His ministry, Jesus brought order to the nation - demons cast out, sicknesses healed, the dead raised and the good news preached. But in their hardness of heart, the Jews now rejected their Messiah and Jesus tells them that their final state will be worse than the first.
We apply this to our situation today in two ways - a public application to the life of this nation and the role of the church and a private application for each of us in our hearts. The great danger of rejecting the word of God and becoming hard of heart is what we must avoid at all costs.