Loss is inescapable in To the Lighthouse, as each character feels the effect of time passing. Moreover, Mrs. Ramsay's death—though just one discrete moment, and conveyed parenthetically—pervades the rest of the narrative.
As a result, the novel's tone is somber, marked by the characters' constant ruminations on the nature of existence and the influence of Mrs. Ramsay's presence—and then absence—in the world. This is embodied well in the middle section of the novel, in a description of the Ramsay's house aging and disintegrating over the passage of time in Chapter 9 of "Time Passes":
Then the roof would have fallen; briars and hemlocks would have blotted out path, step, and window; would have grown, unequally but lustily over the mound, until some trespasser, losing his way, could have told only by a red-hot poker among the nettles, or a scrap of china in the hemlock, that here once someone had lived; there had been a house.
If the feather had fallen, if it had tipped the scale downwards, the whole house would have plunged to the depths to lie upon the sands of oblivion.
Even as there is a constant existential somberness about the novel, seen here in the description of the way in which the house begins to fall apart from neglect, there is also a constant reverence to Woolf's writing. The passage of time and the destruction of the house and the death of Mrs. Ramsay are all vexing and—in their own ways—tragic, but they are also the source of immense beauty. By the end of the book, after all that is happened, Lily Briscoe is finally able to complete her painting; on a higher level, all of these events are the fertile grounds from which Woolf is able to reap her writing. The reverent tone clearly conveys Woolf's view of life's biggest questions as an incredible source of creative and artistic expression.