Claim. Heart is defined as “the emotional impulse to seek joy through love” or equivalently “the emotional impulse that cannot but love” — and it was due to this impulse that God created human beings as object partners of love and all things as object partners of joy.
Elaboration. Lee establishes the definition of heart as the foundation for understanding the four great realms of heart (Concept of Heart). Heart is not merely an emotion or affect but a constitutive impulse — specifically the irresistible impulse to love and through loving to seek joy. The redundancy in Lee’s two formulations (“impulse to seek joy through love” / “impulse that cannot but love”) is intentional: heart is at once teleological (oriented toward joy) and necessary (cannot but).
The theological consequence is creation itself. Because of God’s heart-impulse — the impulse that cannot but love — God created human beings as object partners of love and all things as object partners of joy. Creation is therefore not a free decision among alternatives but the necessary self-expression of divine heart. This is consonant with broader UT teaching that heart is the deepest core of God’s sungsang and hyungsang — the motivation behind the purpose-of-creation.
The “realm of heart” then follows from this definition. As realm of culture means the sphere of influence of a culture, and realm of sovereign power means the sphere of influence of one’s power, so the realm of heart means the sphere of influence of one’s heart. Because heart is the impulse to love, the realm of heart necessarily accompanies and overlaps with the realm of love: “heart and love are two sides of a coin.” The four great hearts (parents’, husband-wife, brothers-sisters, children’s) are therefore equivalent to the four great loves.
This equivalence is doing important conceptual work — it lets Lee move seamlessly between phenomenological descriptions of love-relations and ontological claims about the structure of heart in God and humans. The risk of the move is that any distinction between affect (heart as inner motivation) and act (love as outward expression) is collapsed; critics could press here on whether love can be merely impulsive without judgment, or whether heart should remain a richer category than its expressed love.
See also. heart-shimjung-as-core-of-gods-sungsang, purpose-of-creation-as-joy-through-love, god-is-the-god-of-heart