When a new life enters the world, a new heart enters the world. There is no life apart from a heart, a new life necessitates a new heart. When we become a new, born another, along with that new birth come a new heart. See the new man, must have a new heart ruled by the peace of God. He is to let Christ, the peace of God rule in all things and differences. The word "peace", means to be bound, joined, and weaved together. It means to be assured, confident and secure in the love and care of God. It is to know that God will take care of us no matter what the problem or circumstance, to know that God will not allow anything to swamp or defeat us. But we must realize this peace lies in Christ and Christ alone, and we cannot know this peace unless and until we know and accept Christ in our new heart. It says "let the peace of God rule", this is a command and we must be obedient in order to experience this peace.
This new heart must also be rich with the word of Christ, we are to let the word of Christ dwell in our hearts. The choice is up to the believer, the word of Christ does not naturally dwell in our hearts. Here the word "dwell", means to make a home, to abide or live within. We must make room within our heart for the word of Christ. We must let the word enter our hearts and be at home and make a home there. Christ word must furnish our hearts with all the wealth of its commandments, and promises, instructions and warnings. This will give us a heart of service unto the Lord. As the new man is a servant, he now will have the heart of a servant, he will become a cheerful giver, a willing worker, and a faithful servant unto the Lord. All that is done is done for the glory of the Lord, the spreading of the gospel and the building of His kingdom.
Jesus said you don't put new wine in old skins,so we can't put this new spirit into the old heart.This is the new heart,filled with a new spirit, that goes with our new life in Christ