Explain the poem's allusion to the Seven Sleepers.

The Seven Sleepers of Ephesus is a Christian legend in which seven Christians, persecuted for their faith and sentenced to death by the Roman emperor, are sealed into a cave where they have gone to pray. The men fall into a divine sleep that lasts almost 200 years. When their cave is eventually unsealed, the seven wake. Their experience is seen as proof of the reality of the resurrection of the body.