"When an impure spirit comes out of a person, it goes through arid places seeking rest and does not find it. Then it says, 'I will return to the house I left.' When it arrives, it finds the house unoccupied, swept clean and put in order. Then it goes and takes with it seven other spirits more wicked than itself, and they go in and live there. And the final condition of that person is worse than the first." (Matthew 12:43-45)
These aren't my favourite words of Jesus' teaching and they're likely not yours either. They seem a bit harsh at first read, but they teach an important truth that we need to understand.
Jesus is speaking to our human nature to fill empty places with something. And making it clear that Satan and his demons work the same way, so we need to be aware.
It's a good thing to remove the things in our lives that shouldn't be there. We should deal with sinful thoughts, habits, and actions. We want to remove these things from our lives.
The problem arises when we remove them and then the places they filled in our lives unfilled with anything good. We just choose to leave those places empty. When we remove sinful things from our lives, we need to fill that place with something good and pleasing to God, so that the thing we removed can't come back into our lives.
We can kick Satan and his schemes out, but he will find a way back in if we don't fill those areas where we kicked him out of with something. And when Satan gets back into those areas, he often does more damage when he was there before. That leaves us feeling worse than the time before as well.
If we're not careful, we end up stuck in a cycle of defeat, victory, greater defeat, victory, even greater defeat. With the times of victory growing more infrequent and shorter duration until we give up completely.
That's what Satan wants for us. But that's not what God wants for us.
Jesus doesn't say it in this passage, but other places in His teaching He talks about the Holy Spirit coming to live in all believers. Those places we kick Satan out of should be filled with the Holy Spirit and the things of God. When we allow the Holy Spirit to get into all those places we kicked Satan out of, there is no room for Satan to get back in when he tries.
I believe that Jesus came to be our strength to live as we were meant to live. But that won't happen completely unless we allow Him to access every area of our lives so He can fill every area of our lives.