Since many preachers’ definitions of heart do not include any scriptures, I have to believe they get that from psychology or at least some commentary. That bothers me. My first red flag popped up when one man said the heart is the emotional center. That would be a physical heart if I understand correctly. We ponder, think, and understand, etc. with the spiritual heart but not with the physical. A quick reference list shows that certain qualities (good or bad) are in the heart (Matt. 15:16-19). I am not sure how murder fits in, but it is a quality too. Look carefully at the Hebrew meaning of Prov. 23:7–as a man thinketh in his heart. That is strange, but necessary to understand.
“For as he thinketh in his heart, so is he: Eat and drink, saith he to thee; but his heart is not with thee” (Proverbs 23:7).
OT:8176 sha`ar (shaw-ar’); a primitive root; to split or open, i.e. (literally, but only as denominative from OT:8179) to act as gate-keeper (see OT:7778): (figuratively) to estimate: KJV – think.
It seems to me that Matthew 6:21 explains this Hebrew meaning pretty well. What you accept or allow into your heart is what you are. Those issues are what you present every time you speak.
Conscience seems to be involved with the heart but is not the same as the mind (nous – 3563) because in Titus 1:5 both the mind (3563) and the conscience are defiled.
Proverbs 23:7 actually says that as a man ‘splits’ in his soul, so is he. We can understand from the context that the man’s actions and his inner man are opposites, which no doubt caused the translation to include the heart instead of the soul. This puts a little different light on the Proverb – as a man thinks in his heart, so is he. I have to do some more study on that one!
Matthew 6:21 deals with what we value – our treasure in the sense of what we value. What is highly esteemed among men is an abomination in the sight of God. Men esteem material things, and thus their heart is with those material things. Thus, as a man ‘esteems/values’ in his heart, so is he.
Proverbs 23:7 seems to point more at hypocrisy – what he ‘’splits/opens’ in his soul and his words don’t match. Obviously the Proverb encourages us to be aware of a man’s real value and judgment, which would point to the same thing. This might take more consideration.