Not to go on all-fours; that is the Law. Are we not Men? 
Not to suck up Drink; that is the Law. Are we not Men? 
Not to eat Fish or Flesh; that is the Law. Are we not Men? 
Not to claw the Bark of Trees; that is the Law. Are we not Men? 
Not to chase other Men; that is the Law. Are we not Men?

In Chapter XII, the Beast Folk compel Prendick to join them in the recitation of the Law, a list of quasi-religious commandments that prohibit animal behaviors. The refrain “Are we not men?” serves to remind the Beast Folk that human beings—which they aspire to be—do not engage in such beastly behaviors. But ironically, humans engage in many of these very behaviors repeatedly in the novel, suggesting that the Law serves a more sinister purpose than helping the Beast Folk achieve full humanity. As Moreau later explains in Chapter XIV, the Law has been ingrained in the Beast Folk through hypnotism in order to suppress their natural instincts. The Law serves as a psychological check on the Beast Folk, a system of morality that represses their animal strength and aggression, allowing them to be easily controlled and subdued by the few humans on the island.  

His is the House of Pain. 
His is the Hand that makes. 
His is the Hand that wounds. 
His is the Hand that heals.

In Chapter XII, led by the Sayer of the Law, the Beast Folk chant this mantra in unison as they initiate Prendick into their society. The ominous, indirect references to Moreau via a pronoun (“His”) suggest that Moreau’s name, like the Lord’s, is not to be taken in vain. Likewise the capitalization of Moreau’s “Hand” and “House of Pain” reveals that Beast Folk consider Moreau to be an all-powerful god. Moreover, Moreau is no benevolent god. He rules the House of Pain and wields the power to wound or to heal. The threatening tone of this chant suggests that the Beast Folk obey the Law not out of love or reverence, but to avoid suffering the consequences of Moreau’s wrath.  

“Where is he?” said Montgomery. 

“Beyond,” and the grey creature pointed. 

“Is there a Law now?” asked the Monkey-man. “Is it still to be this and that? Is he dead indeed?” 

“Is there a Law?” repeated the man in white. “Is there a Law, thou Other with the Whip?” 

This dialogue occurs in Chapter XVIII when several of the Beast Folk report Moreau’s death to Prendick and Montgomery. Having believed Moreau to be an immortal, god-like figure, the Beast Folk struggle to understand the ramifications of his death, but they seem intrigued by the possibility that Moreau’s death spells the end of the Law and its restraints. Tellingly, the man in white addresses Montgomery as the “Other with the Whip” when he asks if the Law is still valid. This suggests that the Beast Folk equate the Law with punishment, from which they secretly long to be free.

“Children of the Law,” I said, “he is not dead!” M’ling turned his sharp eyes on me. “He has changed his shape; he has changed his body,” I went on. “For a time you will not see him. He is—there,” I pointed upward, “where he can watch you. You cannot see him, but he can see you. Fear the Law!” 

In Chapter XVIII, in the aftermath of Moreau’s death, Prendick averts a rebellion of the Beast Folk by claiming that Moreau is not dead, a demonstrable lie given that the Beast Folk have just found the body. Prendick’s claim that Moreau has transformed and ascended to heaven reinforces the Beast Folks’ belief in Moreau’s deity and, conveniently for Prendick, buttresses their psychological fear of punishment. The lie of Moreau’s ascension bears an obvious resemblance to the biblical story of Christ’s ascension to heaven after the Resurrection, a not-so-subtle suggestion that real-world religions also employ lies to explain away inconvenient facts that undermine their authority.

“Then I would turn aside into some chapel,—and even there, such was my disturbance, it seemed that the preacher gibbered “Big Thinks,” even as the Ape-man had done.” 

Near the end of the novel, as Prendick struggles to re-assimilate in London, he observes parallels between Christianity and the pathetic religion of the Beast Folk. He compares the preacher’s sermon to the Ape-man’s Big Thinks, nonsense phrases that the Ape-Man liked to repeat because they made him feel intelligent. After Moreau’s death, Prendick had been able to impress and manipulate the Ape-man by teaching him Big Thinks, which the Ape-man would then teach to the other Beast Folk. By comparing the preacher to the Ape-man, Prendick suggests that purveyors of Christianity are unwittingly peddling nonsense designed to control them and their parishioners.