While the bridegroom tarried (Matthew 24:48). We may suppose that all had lighted their lamps at first, in expectation of being immediately called to meet the bridegroom. But he came not. The advent of Christ was not to be as speedy as the disciples imagined.
No one could divine when it would take place. As St. Augustine says, "Latet ultimus dies, ut observetur omnis dies." See here a figure of each Christian's probation. They all slumbered ( ἐνυ ìσταξαν) and slept ( ἐκα ìθευδον) The first verb implies the nodding and napping of persons sitting up at night; the second means "they began to sleep," actually.
All, wise and foolish, did this; so in itself it was not sinful, it was only natural. To such drowsiness the best of Christians are liable. The bow cannot be kept always strung; "Neque semper arcum tendit Apollo."
Having made all preparations, the virgins ceased for a while to think of the bridegroom's coming. The Fathers take this sleep to be an image of death, the awaking to be the resurrection, when the difference between the two classes is known and displayed.
But this would imply that all the faithful will be dead when the Lord comes, which is contrary to 1 Thessalonians 4:17. Nor, on the other hand, is it conceivable that they whose lamps are kept burning till the day of death will be unprovided when the Lord comes.