J.N.D. Kelly, “The Oxford Dictionary of Popes”, (Oxford, UK: Oxford University Press, ©1986) says of Leo:
An energetic and purposeful pontiff, Leo infused all his policies and pronouncements, especially his anniversary sermons, with his conviction that supreme and universal authority in the church, bestowed originally by Christ on Peter, had been transmitted to each subsequent bishop of Rome as the Apostle’s heir. As such, he assumed Peter’s functions, full authority, and privileges; and just as the Lord bestowed more power on Peter than on the other apostles, so the pope was ‘the primate of all the bishops’, the Apostle’s mystical embodiment.
Leo confidently asserted his authority everywhere in the west… (pg 43).
J. Michael Miller, The Divine Right of the Papacy in Recent Ecumenical Theology, described the “process” by which Leo was able to attribute Peter’s “functions, full authority, and privileges” to himself:
Protestant and Catholic theologians agree that Leo the Great (+464) [sic] drew together the threads of a theory on Roman primacy which had been in the process of formation for at least two centuries [emphasis added].
These threads involved the following elements:
1. That the Lord gave [specific rights] to Peter
2. That Peter must have a successor in them
3. That his successor is the Bishop of Rome
The extent of each of these has morphed over time, causing a morphing also of the “papal doctrines”. Each of these will need to be looked at in their specific contexts over time, and also, the relationship of the history to the doctrines will need to be sorted out.
But in the context of “Pope Leo the Great”, it is important to note that in the middle of the fifth century, this is the first time these threads of “papal doctrine” are brought together.
In his theological presentation, Leo taught the dominical institution [the direct institution by Christ] of the papacy in a way which had a great influence on subsequent tradition. His theory explaining the relationship between Christ and Peter, and between Peter and the pope, was at the basis of the classical Catholic understanding of Roman primacy iure divino [by divine right].
Leo based his theory of papal primacy ex institutione divina on the evidence of Scripture: Peter enjoyed a primacy within the apostolic college. Even before Leo’s appeal to the Petrine texts as a justification for Roman primacy, other ecclesiastical writers had already drawn attention to Peter’s leadership role among the apostles.
Here Miller notes, “Although in the first two centuries the Petrine texts were not invoked to justify a preeminence of the bishop of Rome, at the same time there is no evidence that any pre-Nicene writer ever suggested that the religious position of Rome depended on its secular importance.” Later sources – such as the Council of Constantinople (381) and the Council of Chalcedon (451) both attributed “Roman primacy” to its position as the capital of the empire.
It’s important to note, too, that probably the only two early sources to mention Rome as having a leadership position (Ignatius and Irenaeus), it is because Peter and Paul visited the city.
But Ignatius, the champion of what became known as a “monarchical episcopacy” clearly identified a huge gulf between his own authority as a “bishop” and that of the apostles. As well, he never hinted at anything like a “succession”.
And Irenaeus incorrectly asserts that Peter and Paul “founded and organized” the church at Rome. They may have spent some time “organizing” things, but the church at Rome was certainly well-established before Peter and Paul arrived there, and it is virtually a certainty that Peter arrived at Rome after Paul did.
Miller’s note continues, “Once reflection on the reason for Roman primacy began, the Petrine texts provided an explanation for it.” This is a clear example of the kind of after-the-fact explanation of Roman Catholicism that I’ve given in The Roman Catholic Hermeneutic.
Leo interpreted Mt 16:18-19 in such a way that it was Christ himself who gave to Peter personally, and to him alone [emphasis added], a primatial role in the primitive Church. From his reading of the Scriptures, Leo concluded that the Lord gave to Peter, without any human mediation, a real potestas [power] within the apostolic college. Peter’s authority was a sharing in the potestas of Christ. Because of this intimate societas between the Lord and Peter, the apostle’s judgments were considered to be identical with those of Christ.
A second constitutive element of Leo’s teaching on Roman primacy was his theory of the close relation between Peter and the pope. Although the idea of the Roman bishop as successor to Peter was known in the ecclesiastical tradition prior to Leo, such assertions were isolated and not based on rigorous argumentation [bold and italic emphasis added]. Leo clarified his understanding of the link between the pope and St. Peter by using the legal concept of heredity. In the tradition of Roman law familiar to him, the haeres [heir] was acknowledged as having the same rights, authority and obligations as the one whom he replaced. Legally there was no difference between the heir and the deceased. Leo adapted this idea to the authority received by Peter from Christ: the plenitude potestatis which had been given to Peter was also given fully and immediately to each of his successors. As his haeres, the pope enjoyed the same office as Peter. He took Peter’s place in his absence.
Because he held the pope to be the vicarius Petri, Leo was able to bridge the gap between two fundamental ideas: the pope’s inheritance of Peter’s potestas and Peter’s continuing role in the Church. When the term vicarious was applied to the pope, it implied the identity and continuity of Peter’s office. The bishop of Rome was both successor and vicar of St. Peter. As such he received more than a delegation of power to substitute for Peter in his absence. The designation implied the active transcendent intervention of Peter who continued to hold a permanent office in the Church.
A Bridge Too Far
The mechanism by which all of this was supposed to have worked was a complete fabrication. As Steve wrote in his post entitled “Back to Babylon”, far too many things in this account are left unsubstantiated:
From Peter to papacy—a bridge too far:
Mt 16:18 is the primary Petrine text. But a direct appeal to Mt 16:18 greatly obscures the number of steps that have to be interpolated in order to get us from Peter to the papacy. Let’s jot down just a few of these intervening steps:
a) The promise of Mt 16:18 has reference to “Peter.”
b) The promise of Mt 16:18 has “exclusive” reference to Peter.
c) The promise of Mt 16:18 has reference to a Petrine “office.”
d) This office is “perpetual”
e) Peter resided in “Rome”
f) Peter was the “bishop” of Rome
g) Peter was the “first” bishop of Rome
h) There was only “one” bishop at a time
i) Peter was not a bishop “anywhere else.”
j) Peter “ordained” a successor
k) This ceremony “transferred” his official prerogatives to a successor.
l) The succession has remained “unbroken" up to the present day.
Steve provides an extensive analysis of each of those statements at that link.