This episode describes the mechanics of an evil spirit leaving someone only to return.
Although it’s being treated as a separate episode by our reading schedule, this episode properly belongs with the previous episode. This episode is the third illustration of a point Jesus began to make earlier in verse 39; the first two illustrations were of Jonah warning Nineveh and the Queen of the South visiting Solomon.
In all three examples Jesus warns us not to squander opportunities to repent.
Note: Since Luke’s parallel account (Luke 11:24–26) offers no additional material over Matthew, it is omitted here.