Abarim Publications' online Biblical Greek Dictionary
The familiar noun καρδια (kardia) means heart; hence English words like "cardiac" and "cardiology." It stems from the ancient proto-Indo-European root kerd-, from which also comes our English word "heart."
In English, the word "heart" primarily denotes the physical organ that pumps blood through the body and only figuratively one's emotions and such. In Greek this works precisely the other way around. In Greek, the word καρδια (kardia) primarily describes one's mental constitution and disposition, and since upset emotions make the heart beat faster, was only secondarily connected to the physical heart. This secondary connection wasn't complete either, since one's emotions were generally thought to reside in one's general inside, or belly: κοιλια (koilia), hence our word colon, which twists and turns when one's heart is nervous (Mark 7:19 contains a medical insight of astonishing depth), or γαστηρ (gaster), hence our many gastro- words and, sure enough, even our word "gas," the uncontrolled release of which may also demonstrate a troubled kardia.
The noun καρδια (kardia) describes the manifestation of the consensual focal point of many freely interacting elements, which arises from this consensus and continues to ensure, govern and elaborate the autonomy of the member elements and their collective behavior in the environment at large. In our articles on λαος (laos) and εθνος (ethnos) we have discussed how nucleosynthesis (the forming of a heart) works, and it's very common in nature. Atoms and cells have hearts, which contain all information that determines and maintains their nature and character and their behavior toward their fellows. Human minds, which are the next step up in complexity, do not simply sit in our heads, but are rather the "body" of things a mind is aware of, and at whose center our head/heart sits.
The curiously misnamed "Second Coming" of Christ does not describe his return from somewhere else because he never left (Matthew 28:20); he just left our sight (Acts 1:11, see Hebrews 12:1 and 1 Thessalonians 4:17). In stead, in the very near future humanity will experience a nucleosynthesis in which the perfect knowledge of all creation (Romans 1:20, Colossians 1:16-17, 2:3) — the getting to know of whom has brought us all the way from Adam to where we are now (1 Samuel 7:12) — will settle within humanity in a form that is compatible with humanity, to continue to guarantee the personal sovereignty and autonomy of all human individuals and to lead humanity to heights of liberty and joy that can now scarcely be imagined (Matthew 5:8, Galatians 5:1).
Our noun καρδια (kardia) meaning heart is used 160 times in the New Testament, see full concordance, and from it derive:
- Together with the important verb γινωσκω (ginosko), meaning to know: the graceful noun καρδιογνωστης (kardiognostes), meaning heart-knower; one who knows the heart (Acts 1:24 and 5:8 only).
- Together with the adjective σκλερος (skleros), meaning hard or hardened: the noun σκληροκαρδια (sklerokardia), meaning heart-hardness; an unwillingness of some governing core to be formed into the shape that the collective whole makes available (Matthew 19:8, Mark 10:5 and 16:14 only). Since in classical households the man represented the governing core and the woman plus her children the governed body, this word also describes a man's unwillingness to consider the concerns of his family: domestic tyranny.
Male sentiments are not only expressed by a man's beating heart and coiling bowels, but also by the animation of his member. A man whose heart-hardness arises in proper response to his wife's advances will be gratefully received, but heart-hardness for selfish reasons may lead to prolonged headaches and ultimately divorce. In other words: long before people divorce, their sexual energies do.
How precisely the circumcision of one's heart (Deuteronomy 10:16, Romans 2:29) corresponds to the circumcision of one's penis (Genesis 17:10-13) has never been properly explained, but there is an obvious connection (also see our article on the "heaviness" of the Lord).