The heart of the believer is very central to walk with God on earth. There are so many things the bible said about the heart. One of the things the Bible said about the heart is that the heart is deceitful and desperately wicked. This is a typical example of the heart of an unbeliever. A man in Christ who has intimacy with God cannot possess such a heart.
Matthew 6:21
For where your treasure is, there will your heart be also.
Another thing the Bible said about the heart is that God is close to the broken hearted. To be brokenhearted means to have a heart that has gone through experiences that makes the heart open and pliable. The Bible also said that out of the abundance of the heart the mouth speaks. This means that whatever you put into your heart will come out of your mouth one day.
Therefore we should put the right things into our hearts. As a believer, our hearts could grow cold and when that happens it begins to entertain things like uforgiveness, anger, and other forms of worldliness. One of the ways to avoid your heart growing cold is to have a working prayer life.