In chapter 9, Tolstoy introduces the central metaphor of the work, that of the sack, which symbolizes the reality of death over the falsity of life.  He explains that Ilyich, in his "stupefied misery," felt he was being pushed through a "narrow, deep, black sack." This must be some kind of vision he receives in a dream, for only after he falls through the sack does he regain his consciousness.  Only after he's broken through does he begin to speak to God directly, and he begins to realize that he hasn't lived his life has he ought.  This sack is truly a metaphor for Ilyich's deeply personal, spiritual journey through life.  Only when he falls through does he find atonement in the forgiveness of his Lord.

Spiritually, the sack is a metaphor for a woman's birth canal.  It's symbolic of Christ's words in John 3:3, that one must be "born again." Ironically, Ilyich isn't born in this way until he is very near physical death.