The first of two letters ascribed to Pope Cornelius is pretty light on content. Some introductory passages come from the register of Gregory the Great, but the rest of the letter comes from two sources: All the generally pastoral and vaguely pious passages come from a few letters of Pope Martin I, and the rest of the content is based on the Cornelius biography that occurs in the Liber Pontificalis.
We begin with some pretty straightforward exhortations to charity (these from Gregory). There's a bit of a disjunct between these passages and the ostensible purpose of the letter, which is to inform all the faithful that he has supervised the translation of the bodies of Peter and Paul from the catacombs. Here Pseudo-Isidore is just building on the Liber Pontificalis biography. From there he skips on to complain about the Novatian heresy, here also taking his cue from the LP. Wherever God closes a door he opens a window, though (I'm pharaphrasing here), and he rejoices that a variety of confessors who had earlier left the faith have now returned. Naturally, this means that nobody should give up on exhorting the Novatian heretics back to the way of truth.
The rest of the letter is borrowed from Martin. Nothing can separate us from God's charity; we need patience to overcome our adversaries; everyone should remember the eternal rewards that come with martyrdom; the faithful should take up the arms of the lord and resist their spiritual enemies. A few lines lifted from Leo close off the letter.
Recipients: all faithful
Date: 7 Sept.
Sources: Gregory the Great, register; Liber Pontificalis; letter of Martin I; letter of Leo the Great
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