I have been having a friendly discussion (not a debate, thank God) on whether or not the Orthodox teaching on theosis is just another way of talking about the Roman Catholic dogma of purgatory. It is sometimes attributed to “Byzantine”/Eastern Rite Catholics that differences on these things are a question of semantics. Nothing could be further from the truth.
The problem here is that there are at least two radically fundamental differences with which to begin discussing this topic: the nature of God and, concomitantly, the nature of salvation. Apart from some understanding on what’s at stake with these differences one cannot really begin to address whether or not St Mark of Ephesus’ answer to the Florentine prelates does or does not address whether Orthodox believe in purgatory as Roman Catholics believe in purgatory. Of course, individual persons and scholars will nuance this or that aspect of these concepts, but in general the differences play out along these general lines.