There is no official sentence, but three from the book itself gather what it says: the past life of Ivan Ilyich was the simplest, the most ordinary, and the most terrible; perhaps I have not lived as I should have?; and, at the end, in place of death there was light.
The first is the narrator's, at the start of chapter II, and it is the judgment given before the biography: the terrible life has no terrible event, the horror lies in its simplicity. The second is Ivan Ilyich's, in chapter IX, when the question comes to him suddenly and he dismisses it at once, because he did everything as one should. The third closes the crossing: the habitual fear of death is not there, because death was not there either, and in its place there was light.
One sentence deserves care, because on its own it sounds like consolation or resignation: We shall all die. Why should I not make an effort?, said by Gerasim when the master tells him to rest. In the text, the narrator explains that he does not tire because he looks after a dying man and hopes someone will look after him in his turn. There are two readings: simple charity, or the reciprocity of one who knows that death belongs to everyone.