Heart-ology: that subject of all Jesus' teaching
In discovering and building one's relationship to God the central location for hard work and "bottom line" is one's heart. But this choice of word brings up images of the body's pumping mechanism, of Valentines cut outs and stories of romance or feats of loyalty. So rather than say 'heart' perhaps a better word is "one's core or deepest center."
[emotional or moral center, as contrasted with intellectual response; one's personality or disposition]
Consider the many forms and expressions that include the word 'heart'.
Hearty, heart-felt, heart-rending, heartless, good-hearted, cold-hearted, warm-hearted (cold hands warm heart), take heart, disheartening, heart of the matter, heart-and-soul, big hearted, chicken hearted, tender (soft) hearted, hard hearted, in my heart of hearts (innermost heart), evil hearted, black hearted, heart weary, heavy hearted, heart sick, heart breaking, heart to heart, lose heart, play with heart, learn by heart, take to heart
In summary, the task before each person who seeks to know God's character and thus develop the relationship with God has to dwell on what lies in her or his own heart: are actions motivated for self-glory or God's glory, does one go forth to compare efforts to peers or to please God, when reflecting on the results of one's work is it to seek approval (trophies for one's moral scoreboard) or for another reason. As the story of the Widow's Mite tells us (and Paul touches in 2nd Corinthians), the intention and habit of the heart to give to others and to God's glory is the goal. It is what is intended and internal that matters most to God, not the particulars of size or price tag.
So the biggest work while we walk the earth is to discover and then nurture one's affinity to the creator, mainly by attending to what is in one's heart: humble (meek), sincere, ardent and abiding in times that are good and times that are bad. As such the enterprise is about one's core being, one's identity, one's lifestyle (exterior) and approach to the lifecourse (interior)… these three remain: Faith, Hope and Charity [love]. But of these the greatest is Charity.
Each of these key words tie into one's core, one's essence, that which lies in one's heart. FAITH for that which cannot be directly seen or known calls for a calm and resolute heart. HOPE for that which is not yet present or arrived. And CHARITY or LOVE for those around you similarly so engaged in the work of the living of the world, to reach out and encourage (hearten) one another.
We need to be in the business of knowing our own heart, and those of our neighbors; maybe even that of God? In short, we need to know normal developmental stages and maladies that depart from that normal maturation. We need to know what nourishes and that what impoverishes a person's heart. We need to grasp how heart relates to mind; mind to spirit; spirit to soul; soul to body; body to heart.