Whoever has no rule over his own spirit is like a city broken down, without walls. Proverbs 25: 28. Just as a city without walls is unable to stop people coming or going as they please, so having no rule over our spirit means other spirits can come and go as they please. That is not a safe place. We each need to exercise self-control over our spirit, to choose to submit it to the Holy Spirit and partner with Him to stand up to any other spirits that come our way, to take authority over them. This builds a wall that protects us. As we do this we can learn to discern what is happening spiritually around us, and who to let in and who to keep out.