I think Mackey is utterly correct to note that attempts starting in the middle of the last century to to bring grace "closer to, if not fully into, the natural world and its history, where its presence and power would be more accessible to all," were truncated due to the suspicion heaped on them and increasingly even fear. The first such attempt was by Henri de Lubac's Surnaturel, which was promptly placed on the Holy See's Index of Forbidden Books with de Lubac himself being censured and silenced by the Holy Office, the precursor to the Congregation for the Doctrine of the Faith. To be fair to the Holy See, de Lubac died a cardinal of the Holy Roman Church, having been created a cardinal by Pope John Paul II, along with both Yves Congar and Von Balthasar, the latter of whom died before the consistory at which he was to be elevated to the Sacred College convened.
What ran de Lubac afoul? Mackey states the matter rather succinctly: "for arguing for continuity between between nature and grace." Mackey, rightly I think, claims that Karl Rahner (de Lubac's fellow Jesuit), took a lesson from de Lubac's experince and posited "that nature was a 'remainder concept.'" What Rahner meant by "remainder concept," according to Mackey, is "that God had from the beginning of creation destined humanity for a supernatural destiny, a return to a union with God called the beatific vision, and for no other goal." Here is where we encounter Rahner's distinctive existential Thomism. The necessity for even grace to be existential, that is, part and parcel of the world human beings inhabit, is a sure sign of Rahner once sitting under the tutelage of Heidegger. Hence, the "supernatural existential," as Mackey puts it, is "the inmost thing in concrete human existence in all of its concrete history." In other words, positing a "nature" over and against "supernature" is what is superfluous, or remaindered.
In this regard, it is important to mention Teilhard de Chardin, who, even more than de Lubac and others, was firmly silenced. I think Lawrence Cunningham, in that other book that has transfixed me this past week, Things Seen and Unseen: A Catholic Theologian's Notebook, gets it quite right when he writes that he is ambivalent about aspects of Teilhard's theology and is even more accurate when he insists that because he was silenced and his works during his own lifetime were only available in a Soviet samizdat sort of way, "his ideas never got out into the theological marketplace where they could be critiqued." Indeed, had his writings been allowed to see the light of day, to be peer-reviewed and consequently refined, they certainly would contribute much more to this still important discussion.
Mackey insists, again correctly, that Rahner's "sleight-of-hand" in this instance was very typical of his method, especially when he knew what he was saying might be taken exception to by Rome, particularly the Holy Office. In this case, the unacceptable idea "was that God's presence, power, light and grace was all of it detectable as an innermost existential in our history as part of the natural world." The fact that most of this seems quote uncontroversial to most of us now is evidence that he was on to something.
All of which made me think that while we might naturally assign an affinity between the method of Luigi Giussani and the theology of Von Balthasar, I find that Giussani's uncompromising teaching that the place to start, as it were, is one's own experience and that loyalty to and honesty about your experience is what reveals you to yourself and is the way to God, is very consonant with Rahner's thought and was equally as radical. This is precisely why it ran Giussani into difficulties with his bishop and resulted in him spending a few years in the United States. While in the U.S., he was able to see Evangelical Protestantism, aspects of which moved him and helped him see more clearly what his charism meant, up-close and personally. His was a method in advance of its time and it still is to some degree. It is very off-putting to insist that religion is not merely a source of comfort and rules about how to behave yourself, but the way to encounter reality!
I think both can rest confidently on the writings of St. Paul, particularly the first chapter of his Letter to the Romans and the first chapter of his Letter to the Colossians.