The central message of The Death of Ivan Ilyich is that a life measured only by what well-placed people consider correct can come to an end without having been lived, and that death, by stripping away all defenses, forces one to see this.
The book shows this through scenes, not sermon. Ivan Ilyich does everything as one should (the career, the marriage, the house, the cards), and the narrator sums up this life as the simplest, the most ordinary, and the most terrible. When he falls ill, the technique of excluding the living person and treating the case, which he used in court, is the one the doctor uses on him, and the decorum he served reduces the agony to an inconvenience.
The way out the novella offers is not an argument but a movement: Ivan Ilyich stops defending himself and begins to feel pity for others. In the last chapter, what holds him is the certainty that his life was good; when he lets go of it and pities his son and wife, he finds light in place of death. The discovery fits in a sentence: everything was not that, but one could still do that.
There are different readings of the final light. It may be religious, prepared by the confession and communion of chapter XI, or moral, the discovery that fear yields when attention passes from oneself to others. The novella dates from 1886, written after the religious crisis in which Tolstoy came to reject his own novels, and both readings have support in the text.