I think the way that Paul used the word “heart” is the same way that Jesus used it when he said, “Blessed are the pure in heart for they shall see God.” The “heart” is the core of the person, that which is the core of being at the heart of the individual.
In traditional orthodox Christianity and classical moral theology with foundations in both Judaism and the best of Ancient Greek philosophy, the individual or person is comprised of three aspects:
- the mind or rationality of the person whose proper object is the truth,
- the will of the person whose proper object is what is truly good, and
- the senses or emotional aspect of the person which have as their proper object true beauty.
The “heart” of the person is where these three aspects come together to form the person.
When Jesus says, “Blessed are the pure in heart…” What he is saying is blessed are those who are purely and completely, “with all your heart, with all your mind and with all your being” wholly and completely (purely) seeking the true, the good and the beautiful (aka God.)
So what it is that is “written on the heart” is not merely transcribed onto the emotions, but the mind seeking for the truth, the will for the good and the desires or emotions for the beautiful. So it isn’t purely the emotional aspect of a person which counts as the “heart,” it is all three aspects properly aligned – the mind to the truth, the will to the true good and the senses to the truly beautiful – which comprises the heart upon which all three ends have been “written” by God.
Any attempt to reduce the heart purely to the emotions should be resisted, precisely because the mind is required to identify and seek the truth, and the will to choose what the mind (reason) has helped identify as the proper good, and the senses to desire what the mind and will have made clear is the truly good and proper object of each human desire (the beautiful.)
It is this alignment within the person of mind, will and desires which makes someone “pure of heart,” i.e., where false beliefs are outed, the will is focused on the proper goods, and all desires are refined and purified accordingly.