From The Emergence of the Catholic Tradition (100-600):
No passage in Cyprian’s writings has received more detailed attention than the two versions of the exegesis of these words in chapter 4 of his Unity of the Church: one version seems to assert the primacy of Peter as prerequisite to unity among the bishops, while the other seems to treat the primacy of Peter as only representative of that unity. It seems that the first of these versions came first, chronologically, while the second was a clarification of it issued by Cyprian himself, because Rome was making more of his words than he had intended. But the debate over the ‘papal’ versus the ‘episcopal’ exegesis of Matthew 16:18-19 should not obscure the more fundamental point shared by both kinds of exegesis: the indispensability of the empirical unity of the church, ‘this holy mystery of oneness, this unbreakable bond of close-knit harmony… portrayed in the Gospel by our Lord Jesus Christ’s coat, which was not divided or cut at all… [For] that man cannot possess the garment of Christ who rends and divides the church of Christ.’
In making such an issue of the empirical unity of the church, Cyprian [whose date of birth is unknown; he died in 258 A.D.] was expressing the conviction of the church catholic from the beginning. Heresy and schism were closely related because both of the them violated the unity of the church. It is interesting that in all seven epistles of Ignatius [who lived ca. 35-107 A.D.] the church was explicitly called “holy” only once, while the unity of the church in the bishop was one of the overriding preoccupations of all the epistles, so much so that it seems accurate to conclude that ‘the most important aspect of the church for the apostolic fathers is its unity’ (Grant 1964). It has also been observed that the noun ‘unity’ occurred eleven times in Ignatius and the verb six times, but that neither was found anywhere else in the apostolic fathers. For both Ignatius and Cyprian, moreover, the bishop was the key to authentic unity, and schism was identified as party spirit in opposition to him. Therefore the efforts to superimpose upon the second or third centuries the distinction made by Augustinism and especially by the Reformation between the visible and the invisible churches have proved quite ineffectual, even in interpreting the thought of Origen, whose dichotomy between the heavenly and the earthly churches might seem to have tended in that direction; but on earth there was only one church, and it was finally inseparable from the sacramental, hierarchical institution. This church was, in the striking phrase of Origen, ‘the cosmos of the cosmos, because Christ has become its cosmos, he who is the primal light of the cosmos’ (pp. 159-160).
Pelikan was raised in the Lutheran Church—Missouri Synod and was a Lutheran at the time this book first saw publication in 1971. In 1998, less than a decade before his death, he converted to Eastern Orthodoxy. I can hardly pass any sweeping judgments on the man’s attitudes toward the various Christian traditions, having read far too little of his work; but, from what I’ve encountered of his writings, he seems to have been preeminently fair to Catholicism, Orthodoxy, and Protestantism alike. Perhaps this is why, even with his apparent conviction that Church unity was a universal concern of the early Church, he took his time in becoming Orthodox: he understood that the nature of the Church is far more complicated, historically and spiritually, than the polemicists of any side have often been willing to admit. Rather than hastily attach himself to another communion—even one that he may have felt from an early date to be more in line with the Tradition handed down to the Apostles—he seems to have been content to stay, at least for a time, where Christ was visible to him.
Christians have made a mess of the Church these past 2,000 years, and finding Christ in the midst of it all can at times be rather difficult. I would surmise from Pelikan’s long wait that his relationship with God—despite his erudition—was probably one of childlike trust.