Hardy's narrator is an incredibly clear and active voice within the story, establishing a tone of omniscience. One feels that, upon beginning the novel, the narrator already knows what will happen to Tess and is simply letting events play out as they are predestined. On a technical level, this effect of narrative voice is achieved in two different ways: firstly, through the use of parentheses, within which the narrator will periodically insert a direct comment about the characters' behavior.
Hardy also utilizes a great deal of free indirect discourse in crafting his narrative voice. Free indirect discourse (FID) refers to the mixing of the narrator's voice and the characters' voices in passages where the narrator mediates or comments on something that a character says. An example of this occurs in Chapter 4:
But ever and anon [Abraham's] childish prattle recurred to what impressed his imagination even more deeply than the wonders of creation. If Tess were made rich by marrying a gentleman, would she have money enough to buy a spy-glass so large that it would draw the stars as near to her as Nettlecombe-Tout?
Though it is not in quotation marks, one could imagine Abraham literally asking Tess the question, "If you are made rich by marrying a gentleman, would you have enough money to buy a spy-glass so large that it would draw the stars as near to you as Nettlecombe-Tout?" The question has the tone of a child's voice, despite being mediated through the narrator's voice using free indirect discourse.