Jamieson, Fausset and Brown on 1 Corinthians 15:18

18. fallen asleep in Christ--in communion with Christ as His members. "In Christ's case the term used is death, to assure us of the reality of His suffering; in our case, sleep, to give us consolation: In His case, His resurrection having actually taken place, Paul shrinks not from the term death; in ours, the resurrection being still only a matter of hope, he uses the term falling asleep" [Photius, Quæstiones Amphilochiæ, 197].

perished--Their souls are lost; they are in misery in the unseen world.