The spirit is the part of us where Holy Spirit comes to dwell. It is our "temple" if you will. The soul is the seat of the mind, will and emotions of the individual. It is the personality, the part that reveals his personhood. When we receive Jesus Christ, He comes to dwell in our spirit, and form that point on, we are His, lock stock and barrel, but any demonic strongholds are still in the soul and need to be kicked out. Often a person has deliverance right away, repenting of certain things that they cam attached to, but many, many times a believer's stronghold goes into hiding until growth in Christ encroaches on its territory, and a crisis will ensue for it. That is where many people will seek out help and the right people will be able to detect a demonic stronghold and help be rid of it immediately. Others are not so fortunate, and struggle a long time or for the rest of their lives without receiving freedom.
Here is a small excerpt from
http://www.spiritualwarfaremanual.com/sample-chapter/
Paul talks about such things in
2 Corinthians 10:3-6
1. erroneous beliefs, persuasions, and teachings that lead to “acts of disobedience” (verse 5)
2. religious lies and deceptions the enemy uses to enslave us to his ways of thinking, his attitudes, and actions;
3. false arguments and pretensions that come against a true understanding (the knowledge) of God.
How do we know when we are faced with a stronghold, yoke, or bondage? They reveal themselves through our words and lifestyles:
- We are constantly critical of everyone and everything.
- We minimize or negate true or positive things said about us by others.
- We hide our bad habits.
- Certain thoughts fill us with shame, guilt, or condemnation.
- A particular behavior worsens over time.
- We are driven by our impulses and desires.
We are unwilling to give up particular mindsets because we find security and protection with them. They are familiar to us and we believe there is “truth” in them.
Strongholds, yokes, and bondages can vary from minor to moderate to severe. Extreme forms include mindsets that greatly hinder us spiritually, socially, or physically, such as an addiction. Moderate strongholds may limit our fulfillment in life, yet we can still function effectively. For instance, if we believe that poverty equates to pious humility, we may give all of our money away. Minor thoughts such as the need to protect ourselves by lying can be eradicated through conviction from God, leading to our confession and repentance.
Here is a good description of what a stronghold is:
http://www.greatbiblestudy.com/strongholds.php