John Chrysostom

"Then they also which are fallen asleep in Christ have perished." "And why speak I of you," saith he, "when all those also are perished, who have done all and are no longer subject to the uncertainty of the future?" But by the expression, "in Christ," he means either "in the faith," or "they who died for His sake, who endured many perils, many miseries, who walked in the narrow way." Where are those foul-mouthed Manichees who say that by the resurrection here means the liberation from sin? …

Homily on 1 Corinthians 39 ↗

Theophylact of Ohrid

That is, those who died for Christ and bore witness to Him have perished, if there is no resurrection. And in general, all who died in the faith of Christ and in a life of hardship and affliction have perished, because they were deprived of worldly pleasures, and after this will receive no good thing, if there is no resurrection.

Commentary on 1 Corinthians ↗

Thomas Aquinas

922. – But because someone could say: although faith does not cleanse sins, they can be cleansed by good works. Therefore, he adds a second incongruity, namely, that the dead, who cannot be cleansed in the other life, have perished without hope of salvation. And so, as if concluding, he says: Those who have fallen asleep, i.e., died in hope of salvation, in Christ, i.e., in the faith of Christ, have perished, because in the other life, there are no meritorious works.

Commentary on 1 Corinthians ↗