As his mother, Linda, dies, John calls out, "Oh, God, God, God..." and he repeats this to himself.
John realizes that Linda has died sooner than she normally would have because she has been taking excessive amounts of soma so that she could feel the state of euphoria which she used to feel when she was younger. She has also desired to ease herself from the judgment and the shame that she has felt in the presence of those of the New World to which she has returned. Indeed, the residents of this world have found Linda repulsive because they know that she has actually given birth the old natural way and, unlike others of the New World, she has aged and become fat.
Perhaps, too, John calls out to God because he realizes that his romantic idea of the New World has dissolved, and he perceives the tragic results of a society that desensitizes its citizenry to real human emotions and desires. At any rate, it is a tragic end for his mother who never knew the meaning of real love, real friendship, or real life.
John is also hurt when, before she dies, she mistakes him for Popé and not her son. He begins to despair, too, after his disappointing experience with Lenina in the previous chapter.
"Oh, God, God, God..." John cries as his vision of a romanticized "brave new world" dissolves before him.