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Juggling reading all three depending on my mood at the moment, mostly the middle one. Just got to the part there where universalism is talked about for the first time – AN’s evaluation (certainly not universalistic) is that Rome’s doctrine of purgatory was too much like universalism and too closely connected to the arguments of ancient universalism patristics (including Nyssa) for the Byzantine Orthodox to accept when it started to become a topical problem in the middle of the middle ages.
Before then, he mentions nothing about universalism being an issue required by some popes for Eastern bishops to renounce for returning to Roman communion, though I know at least one or two of the Sources of Catholic Dogma feature this requirement.
The overall impression is that neither purgatory nor universalism was a reunion or schism issue until the 1200s, and that once Justinian jumped on universalism the Byzantines felt they had to follow suit in order to avoid being tarred with the other issues (mostly false in hindsight) attributed to Origen – but they followed suit rigorously (notable exceptions like Maximus Confessor excepted), much moreso than the early Eastern Fathers whom AN acknowledges tended to regard hell, purgatory and heaven as progressive versions of the same state of existence rather than discreetly different states of existence.