In spite of Barth’s attempt to take a hard-line protestant stance on the doctrine of justification—even going into long polemical tirades in his Church Dogmatics—nevertheless, his doctrine of justification has played a prominent role in ecumenical discussions between Protestants and Catholics. The foremost interpreter of Karl Barth’s doctrine of justification in this regard is the Swiss theologian Hans Küng, who attempted to show that Barth and the council of Trent were in basic agreement on all the crucial questions surrounding the doctrine of justification. Barth freely conceded that Küng had done justice to all of the contours of his views on justification. In a letter to Küng, which eventually became a part of the preface to Küng’s book on justification, Barth said:
I here gladly, gratefully and publicly testify not only that you have adequately covered all significant aspects of justification treated in the ten volumes of my Chruch Dogmatics published so far, and that you have fully and accurately reproduced my views as I myself understand them; but also that you have brought all this beautifully into focus through your brief yet precise presentation of details and your frequent references to the larger historical context.
That Barth’s doctrine of justification would ever be used in such a fashion was baffling to him, yet at the same time, delightfully intriguing.
What I say about justification—making allowances for certain precarious yet not insupportable turns of phrase—does objectively concur on all points with the correctly understood teaching of the Roman Catholic Church. You can imagine my considerable amazement at this bit of news; and I suppose that many Roman Catholic readers will at first be no less amazed … All I can say is this: If what you have presented in Part Two of this book is actually the teaching of the Roman Catholic Church, then I must certainly admit that my view of justification agrees with the Roman Catholic view; if only for the reason that the Roman Catholic teaching would then be most strikingly in accord with mine!
After reading Küng’s treatment of justification, Barth came to believe that he had so strongly denunciated the Catholic position on justification because he had so woefully misunderstood it. Barth was, however, aware that perhaps in spite of the fact that Küng had flawlessly interpreted his own teaching, the ecumenical discussions would not be received well by the Catholic Church. Although he was warmly open to Küng’s work, he was not as certain of Küng’s interpretation of the Catholic position as he was of Küng’s interpretation of his own position: “Of course, the problem is whether what you have presented here really represents the teaching of your Church. This you will have to take up and fight out with biblical, historical, and dogmatic experts among your coreligionists.”
This Küng did, but the results were disappointing. The attitude of the Catholic Church up to this point had been to assume that since the doctrine of justification was the main reason for the Protestant split from Catholicism (notwithstanding other disagreements), if one could show that a basic agreement existed between Protestant teachings and Catholic teaching, this would cancel the largest motivating factor for division. But once Küng had given the most persuasive demonstration of such essential continuity, the Catholic church quickly altered their stance, arguing, in effect, “Only when the church’s claims of truth, leadership, and hierarchy are settled can we then draw consequences from the doctrine of justification.” When Küng’s hopes for a substantial reassessment of the justification doctrine were largely ignored in the Vatican II council meetings, Küng followed the Vatican meetings with a critical eye. Disheartened, he concluded that “pope and curia [the papal court] were not willing to accept the critical challenge.”
In spite of the apparent initial disinterest of the Catholic Church, we can only predict that were Barth alive today he would be pleased to find, like Hermann Häring, that Küng’s thesis has had the last laugh. Küng’s approach to the ecumenical dialogue over justification appears to have had a major influence in approach to Protestant-Catholic dialogue which has culminated in what might be considered the most significant ecumenical achievement in Post-Reformation times.
So far his book on justification is not outdated. Better yet, his thesis of that time has received a late justification. Everyone today agrees that the doctrine of justification no longer divides confessions. Differentiating exegetical as well as theological and dogmatic research has strongly confirmed that notion, especially the studies about the Council of Trent. … Since 1999, the state of discussion can be easily and accurately shown in the Joint Declaration of Augsburg with its highly detailed style. … [A]ll seven problem areas, the points of agreement as well as continuing disagreement are meticulously listed. Each single time, however, the conclusion is drawn that the differences no longer warrant a church division.
Not everyone, however, has been as optimistic about the viability of the ecumenical discussions that took place over the similarities between Barth’s doctrine of justification and the Catholic position as interpreted by Hans Küng. Alister McGrath, for example, grants that Küng has at least shown that Barth and Trent are both anti-pelagian, but he censures the hype over Küng’s thesis as reflecting failure to recognize the difference between agreement over how man is justified—by grace through Christ—and what justification actually is.
However, the Council of Trent (1543-63) specifically anathematized a series of propositions which it considered Pelagian. The result is, as Küng has shown, that both Karl Barth and Trent teach a strongly anti-Pelagian Christocentric doctrine of justification. Nevertheless, the question of how man is justified before God does not exhaust the question of justification. … [I]t is highly doubtful whether Küng has demonstrated anything other than that Barth and Trent both hold that justification is primarily a divine act arising through the work of Christ. There are at least four areas in which Barth and Trent are in serious disagreement: namely, the nature of justification ; the freedom of the will; the nature of election ; and the assurance of salvation. Küng fails to ask the crucial question, which is this: What do Barth and Trent have in common that Calvin and Trent do not also have in common? The answer to this question is that Barth and Trent have considerable less in common than Calvin and Trent. … What does it mean to say that a man is justified? It is a trivial matter for Roman Catholic, Anglican and Reformed theologians to agree that man is justified by a divine act of grace through Christ, for to fail to accept this would be to deny the doctrine of their churches as laid down by the Council of Trent, Orange II, the Thirty-nine Articles, and the various confessions of the Reformed churches. … But what is the difference between the unjustified and the justified? What happens in justification? What is justification? It is one thing to agree how something occurs; it is quite another to agree on what the entity in question actually is.
McGrath also believes that Küng “confuses the matter by introducing modern Roman Catholic scholars, whose teaching counts as theological opinion, and not as the authoritative teaching of the Church.”
It is our contention that Küng, by presenting the more theocentric, Bible-oriented section of opinion within Roman Catholicism, and by presenting only those aspects of Barth’s theology of justification which are capable of harmonization with this section, has not represented the true state of affairs. This does not mean that Küng has misrepresented Barth’s theology of justification: rather, we are of the opinion that he has been unduly selective.
Because of the prominent role that Barth’s doctrine has played in the ecumenical discussions, Catholics and Protestants argue over whether Barth’s doctrine was more Catholic in orientation or more Protestant. Bruce L McCormack takes issue with Douglas Harink’s claim that “Barth’s doctrine of justification anticipated in all its essential features Harink’s own version of Paul’s teaching on this subject.” He argues that the defining element of the Calvinistic Protestant doctrine of justification is John Calvin’s notion of double imputation—specifically the notion of an alien righteousness outside of us (extra nos)—that came out of the Osandrian controversy in 1551. The intention of this defining element was to free the grounds of justification from anything God does in us (in nobis)—even if it is by grace—under the conviction that it would undermine Christian assurance.
Barth’s justification is forensic through and through, McCormick argues. In Barth, justification does not occur through the faith of the one justified but in eternity past and consists primarily, as we have already noted, in acquittal. Justification takes place in Christ because it is in Christ that God restores his own righteousness by destroying both sin and the sinner. The justification of man is really Christ’s justification in Barth’s forensic framework. In Barth faith is merely our becoming aware of our justification, not even an instrumental cause. Thus, McCormack concludes that Barth’s doctrine of justification is not only protestant, but radically so, for not even our faith makes it effective for us; only Christ’s faithfulness, death, and resurrection makes justification effective. “Christ’s history is as such our history … [and] participation in Christ is not something that has first to be realized by means of an independent work of the Holy Spirit, but is already real even as the God-man carries out his work.” Barth sees both our being and God’s being “constituted by way of anticipation” in His eternal decision of the covenant of grace in which the God-man takes God’s reprobation and we get God’s mercy. Just because Barth does not use the language of imputation does not remove the element from the heart of his doctrine, McCormack argues, only in his doctrine imputation does not occur at a moment in time when the believer puts his faith in Christ. Rather, it happens in eternity past.
Although Barth’s doctrine has perhaps caused more openness between Protestants and Catholics towards fruitful ecumenical discussion, this has not taken place without serious controversy over whether this should have ever taken place, whether it reflects true agreement between essentials of Protestant and Catholic teaching on justification or naïvety. If nothing else, Küng has inspired a new approach to ecumenical theology that relishes in the areas of continuity between Barth (and Calvin for that matter) and Trent. Whereas Protestants and Catholics in time past were more narrowly aiming their energies at polemical writings that emphasized the areas of disagreement between them, Küng’s interpretation of Barth has caused a shift in focus on appreciation for elements that are similar.
 Karl Barth, “A Letter to the Author,” in Hans Küng’s Justification (Louisville, Kentucky: Westminster John KnoxPress, 2004), lxvii-lxviii.
 “I have been guilty of a thoroughgoing misunderstanding and, consequently, of a thoroughgoing injustice regarding the teaching of your Church, especially that of the Fathers of Trent.” Ibid., lxviii.
 Hermann Häring, “Justification: Then and Now,” trans. Katharina Gustavs, in Justification, xxii.
 Ibid. Häring seems to imply that this was part of the reason Küng ultimately denied papal infallibility, for which the Vatican rescinded his authority as a teacher of Catholic theology.
 Ibid. xxv.
 Alister McGrath, “Justification—’Making Just’ or ‘Declaring Just’?: A Neglected Aspect of the Ecumenical Discussion on Justification,” Churchman, vol 96 no 1 (1982): 44-45.
 Alister McGrath, “Justification: Barth, Trent, and Küng,” Scottish Jounral of Theology, vol 34 no 6 (1981): 525.
 Ibid., 527.
 Bruce L. McCormack, “Justitia aliena: Karl Barth in Conversation with the Evangelical Doctrine of Imputed Righteousness,” in Justification in Perspective: Historical Developments and Contemporary Challenges, ed. Bruce L McCormack (Grand Rapids, Michigan: Baker Academic, 2006), 168.
 Ibid., 191.