"Justice and Judgment" is a big theme in Tess of the D'Urbervilles. If Tess isn't responsible for her actions (she is sent to Trantridge to see the D'Urbervilles against her will; she is a victim of rape; etc.), why does she keep getting punished? This is a question that she asks herself (and the universe) at a couple of different points, and it's a question that the reader has to ask pretty frequently, too. Some literary critics have even gone so far as to call Hardy a sadist for punishing Tess so continually for sins she didn't willingly commit.
By refusing to depict the system of justice that arraigned, tried, and sentenced Tess, Hardy creates an ironic detachment from the action of the final chapter and refuses to make himself or the reader complicit in that system.
Angel comes to realize that justice should not be an inflexible, universal norm to which everyone is held equally, but should be flexible to fit individual circumstances.