Matthew 12:44

Then he saith, I will return into my house whence I came out; and when he is come, he findeth it empty, swept, and garnished.

See comment on preceding verse. The failure of Israel to carry forward the good impulses initiated by the preaching of John and the early popularity of Christ and his teachings became the occasion for a far more terrible thing than mere neglect and casual indifference. In the diabolical intentions of the wicked leaders, coupled with the relative "emptiness" of the people regarding any genuine righteousness, Christ clearly saw that the Pharisees would be able to deceive and command them all in a catastrophic rejection of himself as the Christ. That is why the warning came at that moment, when the evil heart and purpose of the Pharisees had become so evident to Christ.