The word "person" in this verse has been translated from the Greek word ἄνθρωπος (anthrōpos). According to the lexicon this word means "a human being, whether male or female." But how can a spirit go in and out of a human being?
Jesus is speaking of the physical body. The physical body is a vehicle for the living being - a spiritual being or spirit-person - to use on a temporary basis. At the time of death of the body, the living being departs from the physical body. This has been proven in hundreds of thousands of cases of clinical death.
In many of these cases, the spirit-person floats to the top of the room and looks down upon the body. Before the body was revived, they separated from the body and are watching the events unfolding around the body that has been declared dead.
This illustrates that the body is much like a house - we occupy the 'house' of the body for a few decades and then we leave it. We are not the body - we only drive it much as a person drives a car.
This is precisely why Jesus also refers to the house - as a metaphor:
"Then it says, 'I will return to the house I left.'"
So let's get this straight. There is a central spirit-person who will occupy a physical body for a few decades. This is the 'owner of the house' so to speak, because this is the person this particular body was assigned to.
But as Jesus explains above, there are also unembodied spirt-persons - persons without physical bodies. Why?
An unembodied spirit-person is in the dimension of ghosts - the ethereal plane or "arid places" - for a reason. Typically it is because they misused their former physical body somehow. They might have committed suicide for example. Or perhaps they drugged their body or otherwise remained intoxicated much of their lives. In these cases, they may be unembodied as a consequence. For example in suicide, the number of body-years the person cut off through suicide will have to be spent in the ethereal plane. Why?
Because the lifetime of our physical body is determined through our previous activities. While we are constantly altering the lifetime length of our body through our own choices, at any point in time there is a predetermined lifetime that has been coded in.
We might compare this to a car. If we were to run a car continuously without rebuilding the engine or putting in a new engine, a particular car will break down at say, 200,000 miles - depending upon the condition of the car and how its been maintained up until that point. But if the car's engine was rebuilt before it broke down, well that would extend the life of the car.
In the same way, if a person kills their physical body before it breaks down naturally, then the consequence must be that the person is stuck in the ethereal dimension - having to watch the physical world but not participate in it - "seeking rest and not finding it."
Thus we find there are many different types of unembodied spirit-persons who are living in the ethereal plane and stuck having to only observe the physical world - without the ability of taking part in it. This can get pretty frustrating. It is sort of like getting stuck in jail with a TV.
So many unembodied spirit-persons are looking for a vulnerable body to jump into and occupy. How does this happen?
Each of us maintains a grip on our physical body through our brain and nervous system - through a subtle network. But our grip on the physical body may be weakened during intoxication or another addiction, or when the body is unconscious or sick. These periods weaken the grip we have on the physical body, and an enterprising unembodied spirit-person may take advantage of that moment and move on in.
In this case, they may take temporary control over the physical body - often during the intoxication period or otherwise weakened state. This is why some people act radically different or get violent when they are drunk - someone else has moved in for awhile.
Then when the 'owner' gets sober and resumes his grip, he pushes the unembodied spirit-person aside.
In most cases, such an unembodied spirit-person will simply wait around for another opportunity to gain a foothold in the body. But in some, the unembodied spirit-person maintains their grip - requiring extraordinary actions in order to send them away.
Such an unembodied spirit-person may be driven away by some corrective measures - such as the person becoming sober. But as Jesus explains here, if such a person tries to reoccupy a person and "finds the house swept clean and put in order" - basically they have cleaned up their act: then the unembodied spirit-person may find some stronger (more "wicked") partners to break into that body with.
While Jesus is using the number seven - he isn't saying there is some kind of rule that there has to be exactly seven - the idea he is stressing is that it will not be easy to get rid of an unembodied sprit-person.
The concept is also metaphorical. Finding "seven other spirits more wicked than itself" relates to the fact that a person can be possessed on multiple levels.
This relates to the time of Jesus, when every bad habit a person had was referred to as an evil spirit. Does this mean that every bad habit we have is actually due to an unembodied spirit-person occupying our physical body?
It may be that we are the only evil spirit occupying our physical body.
Yes, we cannot escape blame for the decisions we make. We cannot always blame someone else. We are responsible for our decisions. We are responsible for our self-centered behavior.
And Jesus is speaking to this when he speaks of impure spirits as well as a house put in order. In this respect, he is speaking metaphorically.
A house put in order will be a person who has cleaned up their bad habits. And the impure spirit returning with seven "spirits more wicked than itself" is symbolic to the fact that we have little strength to counter our self-centeredness alone. We might be able to clean up a few bad habits. But this is not enough. There will be many more bad habits that can sprout up from self-centeredness - and each has the ability to essentially capture the heart.
This interpretation of Jesus' words relates to the deeper meaning that he applied with many of his teachings and activities.
For example, when he healed people's physical bodies, he would also teach about the need for them to be healed spiritually. Thus the healings stood as a metaphor.
And when Jesus illustrated the power of offering to God with the loaves and the fish - he was feeding people practically but also illustrating how we can be fed spiritually - by worshiping the Supreme Being.
And in this discussion, Jesus is again speaking of a physical matter, but also a deeper matter relating to how we can guard ourselves from even "seven other spirits more wicked than itself."
Jesus confirms this two verses later:
"Blessed rather are those who hear the word of God and obey it." (Luke 11:28)
Jesus is speaking of a relationship here. To "hear the word of God and obey it" means to follow Jesus' teachings: And Jesus' teachings relate to re-establishing our lost loving relationship with the Supreme Being.
When we have re-established that loving relationship with God, this relationship will protect us from "impure spirits." This is because impure spirits don't want to have anything to do with the Supreme Being. Why?
Because an impure spirit is envious of the Supreme Being. An impure spirit doesn't want to worship God. An impure spirit wants to be God.
For this reason, if we are ever afraid of an impure spirit - even if it is ourselves - we can simply sing or repeat God's Holy Names for protection. An impure spirit will be driven away by the worship of the Supreme Being.
Just as the sun's rays will remove darkness naturally, a loving relationship with the Supreme Being will naturally drive away an impure spirit and even "seven other spirits more wicked than itself."
This is why Jesus' most important instruction was:
“ ‘Love the Lord your God with all your heart and with all your soul and with all your strength and with all your mind" (Luke 10:27)