The subtitle of the novel, A Pure Woman Faithfully Presented, leads us to the heart of Hardy's intention. "Faithfully Presented" speaks to Hardy's naturalism: the phrase tells us that, in this book, events will unfold in a universe indifferent to the fate of human begins. Therefore, there will be no contrived happy ending in which Tess's pure heart is rewarded by a beneficent providence, for there is no good God meting out justice in Hardy's worldview.
However—and this is key—Hardy wants us to understand that Tess is "pure." What happened to her—her rape, impregnation, and abandonment—was not her fault. She was more sinned against than sinning. The universe may be indifferent, but Hardy takes aim straight at a society which is capable of change but nevertheless blames the victim and makes life as difficult as possible for a girl like Tess. She is "ruined" and "soiled" when still a teenager because she is innocent and naive, just as a young girl is supposed to be in Victorian culture.
Tess pays to the "uttermost farthing" for being a woman in a society that allows women no leeway for transgressing against its moral code but adheres to a double standard that allow men to be sexually promiscuous while savagely punishing women for the consequences of these acts.