A new heart also will I give you, and a new spirit will I put within you, and I will take away the stony heart out of your flesh, and I will give you an heart of flesh”  (Eze 36:26)

Except ye be born again, ye cannot see the Kingdom of God” Said the Lord Jesus to Nicodemus, but he didn't understand it.  He should have known.  He should have recognized the words of the Lord Jesus and made the leap and recognized Christ through it.

The new heart is given to us when we return to God... (repent and believe)
 
 
How do we use the new heart? 

--By carefully obeying God's Word and the indwelling Holy Spirit.
 
 
Unless we mortify the stony heart, we cannot experience the new heart.  As we stand against our old nature, proportionally we grow in the new.  If we are strong in the old nature, we are weak in the new and vice versa.

Therefore we are buried with him by baptism into death: that like as Christ was raised up from the dead by the glory of the Father, even so we also should walk in newness of life.”  (Romans 6:4)
 
 
Set our will to follow Christ:

--Satan has no room in the new heart, but the old heart has strongholds, and Satan rules there.

If any man will come after me, let him deny himself, and take up his cross daily, and follow me.”   (Luke 9:23)

A.W Tozer:  “Let him deny himself.”  We hear these words and shake our heads in astonishment.  Can we have heard aright?  Can the Lord lay down such severe rules at the door of the Kingdom?  He can and He does.  If He is to save the man, He must save him from himself.  It is the “himself” which has enslaved and corrupted the man.  Deliverance comes only by denial of that self.  No man in his own strength can shed the chains with which self has bound him, but in the next breath the Lord reveals the source of the power which is to set the soul free:  “Let him take us his cross.”   [The cross] was an instrument of death.  Slaying men was its only function. And when it is robbed of its tears and blood and pain it is the cross no longer.  “Let him take... his cross,” said Jesus, and in death he will know deliverance from himself.  (Tozer, 'Salvation Walks the Earth'  The Set of the Sail p. 40-43)
 
The old nature is seated in our 'self'.  It has many strongholds where Satan dwells.  This is so because we have his nature (the fallen nature), we bare his image, we are his seed, and by this  (his) nature we accomplish his purposes. 

A stronghold is a fortified structure which is able to resist enemy forces.  An invading army needs to take down the strongholds to hold the land.

When we die with Christ, we must let the 'strongholds' of our lives be taken down by the Lord, and we can do that by allowing the Holy Spirit to do the work in us.  But, He cannot do it alone, He needs our participation.  So, obedience is the key, and the set of our will to repudiate the old life and side with the new and to act and to talk according to the new; by the leading and by the help of the Holy Spirit.

When we were lost we were under enemy control; our lives were subject to strongholds.  These strongholds were constructed for a purpose.  They were designed to keep us lost; Satan in his war is in the business of constructing strongholds which feed our fallen nature.  His desire is to keep us blind from the Gospel of Christ, so that we perish.

But if our gospel be hid, it is hid to them that are lost: In whom the god of this world hath blinded the minds of them which believe not, lest the light of the glorious gospel of Christ, who is the image of God, should shine unto them.”  (2 Cor 4:3-4)

When we come to Christ the battle for territory has begun.  Satan is not willing to give ground to his enemy, the Lord of Hosts; he does not want us to live a successful spiritual life.  Therefore, his goal is to keep as many strongholds standing in our life as he can, allowing him to wage war on our souls.  Remember, Satan's goal is to prevent the power of God from being established in the believer's life.  He does this through strongholds.  If Satan can establish areas of operation in our lives; he will then have the ability to attack at will.  He can then keep us from being on the offensive against his kingdom.

For this reason it is imperative for us to have these Satanic strongholds pulled down. If we don't remove strongholds we invite defeat in our spiritual walk, because we are giving Satan a base from which to wage war.  The only way that we can assault spiritual strongholds is through the power of the Holy Spirit dwelling in us.  Without the heavenly power in our lives we are at Satan's mercy.  The Holy Spirit through Paul shows us how to wage war:

For though we walk in the flesh, we do not war after the flesh: (For the weapons of our warfare are not carnal, but mighty through God to the pulling down of strong holds;) Casting down imaginations, and every high thing that exalteth itself against the knowledge of God, and bringing into captivity every thought to the obedience of Christ;” (2 Cor 10:3-5)

We walk in the flesh:  We are in the flesh, but this is not where our battle takes place.  We need to look at things from God's perspective; we need to train our spiritual eyes, recognizing the source of this conflict in us.  As God's redeemed children we waste our time with waging war using weapons of flesh because this is not where the battle is.  Paul wants us to understand the nature of war in the spiritual realms.  Many times we can waste our energy focusing on the wrong solutions to a problem.  We might think secular council or therapy or some human action can solve our problems, when the issue is spiritual.

The weapons of our warfare:  In the description of the armor of God, only two offensive weapons are listed.  The shield, breastplate, belt, shoes, and helmet are essential, but they are mainly defensive in nature.  Our offensive weapons are the Word of God, which is the Sword of the Spirit (Hebrews 4:12; Eph 6:17) and prayer (Eph 6:18).

We, the children of God use our God given weapons to pull down or destroy these strongholds.

Using scripture and prayer we have the power of God to overcome strongholds.

For example:  Unbelief is the greatest and most dangerous stronghold.  Our great ego is one stronghold.  Our sovereignty is a stronghold.  Pride is one of the greatest.  Satan dwells in these strongholds, and we have no way to have victory over him unless we pull down that stronghold.  [“Neither give place to the devil.”  (Eph 4:27) is the instruction for us.]  Any kind of addiction is our stronghold.  Our likes and dislikes, fear are strongholds. Laziness is a stronghold.  Self being on the throne is a stronghold.  Our 'right' to anything is a stronghold.  Resentment is a stronghold.  Un-forgiveness is a stronghold.  Our own expectations are strongholds when we plan our own plans instead of trusting the Lord and leaning on Him.  Disappointment, sadness, self-pity are strongholds, bitterness, or to have my own way are strongholds.  To trust our logic/understanding is a stronghold.  (“Trust in the LORD with all thine heart; and lean not unto thine own understanding.” Proverbs 3:5)  We are to pull down false ways of thinking or false reasoning that is not based on Scripture.  We are called to stand against any false logic that is not based on God's Word.  TV, newspaper, magazines... can be strongholds where Satan can get to your heart, he can occupy your thoughts, he can make our thoughts smeared.  Then these sins are all like a barricade between God and us.  They successfully separate us from Christ and from His Word.  They can take away our peace and joy and make us miserable, discontented, unhappy, dissatisfied and angry, thus we give room to the devil.

There can be many different kinds of idols in our lives that are strongholds for Satan.  Try to identify your strongholds.

Josiah was a praised king; he was young when he became king, eight years old.  When he was 16 he began to seek God with a sincere heart and during his reign Judah had a revival.  Both Daniel and Ezekiel were the product of that revival.  Jeremiah cried at the death of Josiah, who was considered one of the most righteous kings of Judah.  What separated Josiah from the others was his sincere heart and his willingness to do what others would not do.  He did not want anything to compete with the Lord, no matter how unpopular it made him, and God blessed his reign.  He removed the 'high places'.

As the children of God, our job is to pull down the idols set up in our lives.  Anything, whether intentional or not, which is placed above God is an idol.

bringing into captivity every thought to the obedience of Christ;” (2 Cor 10:5).  How are these strongholds destroyed?  By bringing every thought into captivity.  Our minds and heart need to submit to the will of the Lord.  Before we can be effective on the spiritual battlefield we must make our thoughts subject to the will of God.

Let the wicked forsake his way, and the unrighteous man his thoughts: and let him return unto the LORD, and he will have mercy upon him; and to our God, for he will abundantly pardon. For my thoughts are not your thoughts, neither are your ways my ways, saith the LORD. For as the heavens are higher than the earth, so are my ways higher than your ways, and my thoughts than your thoughts.”  Isaiah 55:7-9

O Jerusalem, wash thine heart from wickedness, that thou mayest be saved. How long shall thy vain thoughts lodge within thee?”  Jeremiah 4:14

It is very important to recognize our strongholds and to have a determination of the will to withstand them, and to pull them down through the power of the Holy Spirit, since we know who is hiding in the strongholds of our lives.