What struck me in Hillebert's introduction to the book was how similar de Lubac's project was to mine in The Shape of Joy.
As Augustine famously put it, our hearts are restless until they rest in God. According to de Lubac, this restlessness is due to our natural longing for a supernatural end. Nature itself cannot fulfill this desire. Consequently, at the heart of human existence is a chronic thirst and hunger, a persistent dissatisfaction that nothing in this world can satisfy.
This is, incidentally, C.S. Lewis' famous argument from desire. All natural desires—think of hunger, thirst or sex—point toward toward their natural satisfactions. And yet, there is a desire that cannot be fulfilled by anything in this world. Thus, there is an unfulfilled desire—Lewis called it "Joy"—that points beyond nature and toward supernature.
Noting this in de Lubac's work, Hillebert argues that there is a organic connection between theology and apologetics. This is where the connection with The Shape of Joy shows up. Specifically, theology points to and explains the origins of our inner restlessness. And our experience of this restlessness, acutely and chronically, corroborates the theological account. Faith aligns with felt human experience. Theology is its own apologetics.
Here is Hillebert:
Human being is teleologically ordered to an end that infinitely surpasses the powers of nature to attain. Humanity’s essential restlessness is the ontological sign of this disproportion between human nature and humanity’s vocation. As I will argue throughout, this insufficiency of human nature and the inquietude it engenders leads de Lubac to insist on the necessary compenetration of theology and apologetics—on, that is, the immanently compelling character of the church’s dogma. The “proof ” of Christian revelation is not something external to it. Revelation’s truthfulness is guaranteed by its own content, by what Erich Przywara describes as “the internal coherence of the vision of the world proposed by faith.” A hermeneutics of human existence operating under the impulse of this compenetration of theology and apologetics will thus seek to demonstrate the extent to which human existence is ultimately unintelligible in abstraction from the revelation of humanity’s supernatural vocation. The efforts of “pure reason” to secure the meaning of human existence terminate at the acknowledgment of reason’s own insufficiency. Only the revelation of God reveals us to ourselves.
This is how The Shape of Joy functions as Christian apologetics. The Shape of Joy uses the research of positive psychology to show how human flourishing is experienced through a relation with transcendence. As de Lubac would put it, positive psychology empirically documents our natural desire for a supernatural end. Or, as C.S. Lewis would put it, the psychological research describes how our joy comes from something found beyond (transcendence literally means "to go beyond") the natural world.
