Shelley uses William's death in the fictional novel Frankenstein, to show how Victor is illuminated and realizes that there are no pure creations that mankind can make.
When Victor is sleeping after he creates the monster, he starts to have a different point of view in his creation. In the novel it says, "I thought I saw Elizabeth...in the folds of the flannel" (pgs.51-52). The dream he has of seeing his mother's corpse makes him see that reviving deceased people is inhuman and should never be done.
William's death is a turning point for Victor. In the novel Victor's father sends him a letter saying, "William is dead!...Victor he is murdered!" (pg.64). Victor is illuminated by irony. His brother William, as pure and innocent as he was, was murdered by the monster that is supposed to be his pure creation.
William's death makes Victor see that his life has changed in a negative way. in the novel it is mentioned, "...but now misery has come home,...each other's blood" (pg.91). Victor is finally conscious of the consequences that his actions have made in his life and how it has affected him. By Victor mentioning "misery" it shows that he regrets what he has done.
The meaning as a whole is that there is no pure creation when dealing with life. Humans shouldn't try to be something that there not because it never turns out how they want it to and it ends up harming the people who are loved.