This is an idiom used often in reference to the most important aspect of an issue, or the problem at hand. For example: “Thank you for coming. I’m going to skip all of the preliminaries and go right to the heart of the matter; our company is losing money, and it is being taken by someone inside.” The heart of the matter here, is that money is being embezzled by an employee.
As for the person who is taking the money, there is another issue, another heart of the matter, namely, he has stooped to the level of a thief. In the case of every wrong doer, the heart of the matter is always rooted in his innermost being. The Bible speaks of this inner self as one’s heart. (Not the blood pumping organ, but the deep recesses of the mind)
Several references reveal some interesting truths about the “heart” of man: And GOD saw that the wickedness of man was great in the earth, and that every imagination of the thoughts of his heart was only evil continually. (Genesis 6:5) “The heart is deceitful above all things, and desperately wicked: who can know it? (Jeremiah 17:9)” “A good man out of the good treasure of his heart bringeth forth that which is good; and an evil man out of the evil treasure of his heart bringeth forth that which is evil: for of the abundance of the heart his mouth speaketh. (Luke 6:45)” King David of old pleaded with God, “Create in me a clean heart, O God; and renew a right spirit within me. (Psalms 51:10)” …and He did!
Hope for the depraved heart of man is found in Jesus Christ, who purchased our pardon with His blood. Interested? First, change your mind about sin and God, and then, “…if thou shalt confess with thy mouth the Lord Jesus, and shalt believe in thine heart that God hath raised him from the dead, thou shalt be saved. For with the heart man believeth unto righteousness; and with the mouth confession is made unto salvation. (Romans 10:9-10)”
If you will give attention to the heart of the matter, God promises, “Eye hath not seen, nor ear heard, neither have entered into the heart of man, the things which God hath prepared for them that love him. (1Corinthians 2:9)”