During the course of Chapter 1, Parson Trigham informs Jack Durbeyfield that he is part of the revered D'Urberville line. Mr. Durbeyfield responds to this revelation with a characteristic idiom:
"Daze my eyes, and isn't there?" said Durbeyfield. "And here have I been knocking about, year after year, from pillar to post, as if I was no more than the commonest feller in the parish . . . "
The idiom "from pillar to post" essentially means "hither and thither," implying that he has been aimlessly traveling all over the place. Jack Durbeyfield is a haggler—a middleman in vegetable markets in London, a "huckster" of green produce. This idiom conveys details to the reader about his pseudo-nomadic, working-class lifestyle.
Furthermore, Jack Durbeyfield's use of idiom marks him as lower in social class than certain other characters—like, for instance, Parson Trigham. Linguistic markers of socioeconomic status are important in the Tess of the D'Urbervilles. Hardy takes great pains to insert idiomatic phrases throughout; these consistently indicate a character's level of education, which is important in mitigating social interactions in the novel. Jack Durbeyfield's pretensions towards grandeur in the first part of the novel seem comical, in part because is lack of education and material wealth make it such that other characters—perhaps even the reader—might consider him their social inferior.
In Chapter 34, the narrator uses an idiom to describe Tess, who is dressed up in Angel’s godmother’s jewels:
As everybody knows, fine feathers make fine birds; a peasant girl but very moderately prepossessing to the casual observer in her simple condition and attire, will bloom as an amazing beauty if clothed as a woman of fashion with the aids that Art can render; while the beauty of the midnight crush would often cut but a sorry figure if placed inside the field-woman’s wrapper upon a monotonous acreage of turnips on a dull day.
The idiom “fine feathers make fine birds” ties in well with the broader themes of the novel, especially with the contradiction of traditional class hierarchies. “Fine feathers” are the equivalent of social niceties—expensive clothes, fine jewelry, a fancy education. These things can give any person, regardless of character, the appearance of elegance. Those who appear elegant (in Hardy’s terms, the “fine birds” of society) are thus enabled because they have political power and monetary resources. This does not mean, however, that those of a higher social standing are morally superior. The narrator’s use of idiom in this context implies that Tess is no better or worse than anyone else; she simply does not have the means to appear elegant and refined.