When the Lord saves us, he takes our deceitful heart that is desperately wicked and replaces it with a new heart.
Ezekiel 36:26-27 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. And I will put my spirit within you, and cause you to walk in my statutes, and ye shall keep my judgments, and do them.
A New Heart
When the Lord saves us, he takes our deceitful heart that is desperately wicked and replaces it with a new heart. He also takes our dead spirit and quickens it and gives us a new spirit. It is so important for a Christian to keep their heart on course and right with God. I realize this passage is talking about the nation of Israel in the millienum but it still applies to us spiritually. You did not have the ability before salvation to overcome the power of sin. A new heart allows you to make godly decisions that your deceitful heart would not allow. You still need to guard your new heart because it can still be deceived if you let it. You need to keep that heart on course with God diligently. Just like a ship needs to be kept on course, so does our heart. You steer a ship and your steer or control your heart with the help of God.
A New Spirit
You also have a new spirit to work in concert with your new heart. The two work together. Your new spirit and new heart allow you to make right decisions. In order for you to make wrong decisions now, you must override the new spirit that lies inside of you. As a general rule of thumb, it is not good to hit the override button on equipment and just keep going. Eventually you will damage something. Machines have built-in safety features that shut them off before they break. The same is true of a Christian. The Holy Ghost of God tells your heart to stop before you break yourself with sin.
A Heart of Flesh
God said he would replace our stony heart with a heart of flesh. Stone is dead. Flesh is alive. Stone cannot react to pain or feeling. Flesh can react to both. We now have the ability to feel the effects of sin and react to it. We can say that it “hurts” and stop it. Before you were saved you sinned and it did not bother you a lick. That is your stony heart. Your heart now can make the right decisions because it is now alive. The spirit of God quickens us or makes us alive. God keeps our heart alive and fresh to Him everyday as we seek His face. If we keep our heart on course with God, we will be able to deal with all of the issues that life throws at us.