“The heart is deceitful above all things,
And desperately wicked;
Who can know it?
10 I, the Lord, search the heart,
I test the mind,
Even to give every man according to his ways,
According to the fruit of his doings.”
The Scripture clearly shows the connection between the heart and the mouth: “Out of the heart the mouth speaks.” (Matthew 12:34)
However often in professional situations this is not the case at least in my observations. The constraints of professional conduct cause doctors and other professionals to speak the logical truth arising from their analyses rather than what they might think in their hearts about the person they are dealing with. Similarly, a salesman will not express his heart very often if he wants to make a sale.
This is not always a bad thing. We can’t often do what we want nor should we. Jeremiah records God saying that the heart is desperately wicked and deceitful above all else and that no one but He can understand it (Jer. 17:9).
Jesus said that it was out of heart that all forms of wickedness arise (Matthew 15:18). Paul and James talk about the flesh and the Spirit being in opposition so that you can’t do what you want to (Galatians 5:17, James 4:4-6). At the end of Romans 7 Paul says the secret is to do what Jesus says which is the same as walking in the Spirit and not in the flesh.