John Calvin Commentary 1 Corinthians 15:18

"Then they also that are fallen asleep in Christ have perished." — 1 Corinthians 15:18 (ASV)

Then they who are fallen asleep. Intending to prove that if the resurrection of Christ is taken away, faith is useless, and Christianity is a mere deception, he had said that the living remain in their sins. But as a clearer illustration of this matter is seen in the dead, he presents them as an example.

“Of what advantage would it be to the dead that they once were Christians? Therefore, our brothers and sisters who are now dead lived in the faith of Christ to no purpose.” But if it is granted that the essence of the soul is immortal, this argument appears, at first sight, conclusive. For the ready reply will be that the dead have not perished, since their souls live in a state of separation from their bodies.

Therefore, some fanatics conclude that there is no life in the period between death and the resurrection, but this frenzy is easily refuted. For although the souls of the dead are now living and enjoy quiet repose, yet the whole of their blessedness and consolation depends entirely on the resurrection, because their well-being is based on this alone: that they await that day when they will be called to the possession of the kingdom of God. Therefore, regarding the hope of the dead, all is lost unless that day arrives sooner or later.