Letter III is the operative annulment that Letter II had set up. The Vienne dispute, brought to Rome by Aeonius through the presbyter Crescentius, has been heard with both parties’ positions presented; Symmachus has reviewed the older Apostolic discipline; and he now annuls Anastasius II’s ruling and orders the restoration of the older practice. The letter’s operative significance is canonical-jurisdictional in the strict sense — it is one pope formally voiding a particular ruling of his immediate predecessor — and its theological argument is among the most compressed and powerful in the late-fifth-century corpus.

The Trinitarian analogy in Chapter II deserves close attention. The argument runs: the Trinity has one undivided power across three Persons; the priesthood (and within it, the See) is exercised by successive bishops; therefore the priesthood is one and the same across successive holders, just as the divine power is one and the same across the Persons. The unity of the See across time is grounded not in human institutional continuity but in a structural likeness to the Trinity itself. The reader should observe what this analogy entails. If the priesthood is one across successive bishops in the way the Trinity’s power is one across the Persons, then each successor wields the same office and acts with the same authority as those before him — including the full power of binding and loosing. What follows from the unity is not that successors are constrained from exercising the loosing power, but that they exercise it as wise stewards of an office whose unity across time is part of its dignity. Carelessly undoing what predecessors have established would destabilize the unity of the office; preserving what predecessors have established expresses that unity. The Trinitarian analogy thus grounds not a constraint but a characteristic mode of exercise: ordinarily preserve, depart only for grave cause.

The vicars-of-Peter passage in Chapter III is theologically and canonically central. Symmachus invokes the title vicarii beatissimi Petri apostoli of his predecessors collectively, and the rhetorical question — “what reverence will be judged due to the vicars of the most blessed Apostle Peter if what they shall have established is dissolved when they depart from life?” — does substantial work. The reverence owed to the vicars of Peter is reverence to Peter’s own authority exercised through them. What they establish is established by Peter; what would be dissolved at their death is in fact something that participates in Peter’s perpetual authority. The argument is the structural complement to the binding-and-loosing principle: the See that binds is the See that looses, but what successive vicars of Peter validly establish is preserved by Peter’s own authority across the succession.

The reader should observe how the letter’s operative action — the annulment of the Anastasian ruling — fits within the framework of perpetuity and the binding-and-loosing power. The pope holds the full power of the keys; he can loose what his predecessors have bound. Symmachus is not constrained by Anastasius II’s ruling; he annuls it by his own authority. What the letter sets forth is his prudential judgment for doing so: the predecessor’s ruling had been obtained by stealth procurement and conflicted with the older Apostolic discipline; the unity of the priesthood across time is best preserved by maintaining the older sanction; the office’s characteristic mode is preservation, with departures reserved for grave cause. Anastasius II’s particular ruling is loosed by Symmachus because, in his prudential judgment, the cause was not grave enough to warrant it and the procurement was not clean. The annulment is thus an exercise of Symmachus’s own authority — the same authority Anastasius II had — directed by the considerations a wise occupant of the See takes into account when deciding whether to preserve or to loose what predecessors have established.

The reader who has followed the corpus from Felix III through Anastasius II to Symmachus will recognize that the Vienne dispute is not an isolated case but an instance of a recurring pattern. Each pope is exercising the See’s discipline in continuity with his predecessors; occasionally a particular ruling is found inconsistent and reviewed; the principle of continuity is preserved by the act of review itself. The argument here in Letter III sets out, with unusual theological compression, the structural framework within which all such reviews operate: the unity of the priesthood across time, the perpetuity of what is established by the vicars of Peter, and the moderation of new desires by reverence for antiquity.