Matthew 12:44

‘Then he says, “I will return into my house from where I came out”, and when he is come, he finds it empty, swept, and furnished.'

So the spirit decides that it will try to repossess its house, and when it returns it finds it empty. The power of the Spirit which drove it out (Matthew 12:28) is no longer present in the house. It is, however, unsuitable for habitation by the likes of an unclean spirit, for it is swept and scrubbed, (or furnished). It is clean. So it recognises that it will need reinforcements.