Tess of The D'Urbervilles

"Tess of the D'Urbervilles" tends to be a little slow at first but then picks up. What I got out of the story is that this man finds out about his ancestors but I dont understand why they are so important. Then she meets the D'Urbervilles. This family all seems kind of strange in a way. Why would you just change your name after you retire? Maybe because your hiding something? I'm not quite sure if I understand why he baby died? Overall the story is very good although a little confusing.