For example in A Room With A View, by E. M. Forster, the tenses suddenly change from past to present or vice versa:
The Sunday after Miss Bartlett's arrival was a glorious day, like most of the days of that year. In the Weald, autumn approached, breaking up the green monotony of summer, touching the parks with the grey bloom of mist, the beech-trees with russet, the oak-trees with gold. Up on the heights, battalions of black pines witnessed the change, themselves unchangeable. Either country was spanned by a cloudless sky, and in either arose the tinkle of church bells.
The garden of Windy Corners was deserted except for a red book, which lay sunning itself upon the gravel path. From the house came incoherent sounds, as of females preparing for worship. "The men say they won't go"—"Well, I don't blame them"—Minnie says, "need she go?"—"Tell her, no nonsense"—"Anne! Mary! Hook me behind!"—"Dearest Lucia, may I trespass upon you for a pin?" For Miss Bartlett had announced that she at all events was one for church.
The sun rose higher on its journey, guided, not by Phaethon, but by Apollo, competent, unswerving, divine. Its rays fell on the ladies whenever they advanced towards the bedroom windows; on Mr. Beebe down at Summer Street as he smiled over a letter from Miss Catharine Alan; on George Emerson cleaning his father's boots; and lastly, to complete the catalogue of memorable things, on the red book mentioned previously. The ladies move, Mr. Beebe moves, George moves, and movement may engender shadow. But this book lies motionless, to be caressed all the morning by the sun and to raise its covers slightly, as though acknowledging the caress.
Presently Lucy steps out of the drawing-room window. Her new cerise dress has been a failure, and makes her look tawdry and wan. At her throat is a garnet brooch, on her finger a ring set with rubies—an engagement ring. Her eyes are bent to the Weald. She frowns a little—not in anger, but as a brave child frowns when he is trying not to cry. In all that expanse no human eye is looking at her, and she may frown unrebuked and measure the spaces that yet survive between Apollo and the western hills.
What is the purpose for the changes? It made me confused about when the event takes place.