After the death of the dog, Neville resists the temptation to drink heavily. Instead, he returns to work trying to understand the vampires.
Strangely, Neville doesn’t sink further into depression after the dog’s death; instead, the dog’s death inspires him to work harder.
Neville remembers a year ago, just a few days after he put Virginia to “her second and final rest.” During the day, he wanders through the streets, and encounters a man who tells him, “come and be saved, brother.” The man leads him to a tent, in which a “frenzied” crowd of people is joined together in prayer. The people pray that God will protect them from the vampires. A preacher yells out that God is punishing human beings for their sins by sending vampires to torment them. Neville manages to leave the tent; by this time, night has fallen.
Notice that Matheson doesn’t describe Virginia’s second death (although, presumably, Neville is forced to kill her). The passage also seems to criticize organized religion, describing the crowd of spectators as “frenzied” and masochistic, since they’re willing to blame themselves for vampirism. While religious fanatics accept the plague as an inevitable punishment from God, Neville tries to remain rational.
Back in 1976, Neville sits in his living room, reading about psychology. It occurs to him that some of the vampires’ behaviors—for example, their aversion to the cross—could be psychological, not bacterial in origin. During the vampire plague, there was a massive religious revival, and millions of people engaged in “primitive worship.” So, perhaps, when these worshippers themselves contracted the vampire germ and woke up as vampires, their minds snapped. Neville realizes that vampires may not like crosses and mirrors because the sight of a cross reminds them of their previous lives as religious fanatics, while mirrors remind them of their new vampire identities. He also realizes that some of the “vampires” believe themselves to be vampires, because religious leaders and yellow journalists taught them to hate and fear vampires during their final days as human beings. This would explain why the vampires outside his house never try to burn down his property—they can’t think logically.
Neville’s hypothesis is that the vampires who torment him every night were once religious fanatics (“primitive worshippers,” as Matheson calls them), who were told that vampires are demonic—now that these fanatics have been reborn as vampires themselves, the contradiction causes them to go insane. The passage could be interpreted as Matheson’s critique of organized religion in general: he seems to be implying that religion, through its intensity and hysteria, has actually made the vampires more dangerous and unstable. Matheson further criticizes organized religion by drawing a clear parallel between the hysterical mob of worshippers and the mob of vampires.
Neville pauses for a moment and realizes that his life is becoming slowly more bearable. Despite the death of the dog, he’s feeling optimistic about the future. He spends the evening listening to phonograph records and relaxing while, “outside, the vampires waited.”
In contrast to organized religion, science and rationality calm Neville and give him a sense of purpose: he intends to use his new psychological and medical knowledge to fight vampirism.