James now compares the kind of faith that is not demonstrated in action to the faith the demons have. To open the argument he cites the central article of the Jewish faith, which both he and his opponent subscribe to.

You believe that God is one: there are some textual variations here, but they make little difference in the meaning. The Revised Standard Version rendering is a statement of fact; Contemporary English Version has a similar rendering: “You surely believe there is only one God.” Trying to bring the sense out more forcefully, some translations have rendered it as a question; for example, “Do you believe that there is only one God?” (Good News Translation; so also Translator’s New Testament) or “Do you believe in one God?” (Goodspeed). It can also be rephrased as “Do you believe that ‘God is one’?” The expression believe that appears to indicate that what the author has in mind about believe is not the more usual sense of personal trust and commitment but an intellectual consent and commitment to the content of belief, namely God is one. This confession has its origin in the Jewish Shema (“Hear, O Israel…,” Deut 6.4) and is used also by Christians (Mark 12.29; Rom 3.30).

The belief in this confession is not bad or wrong, as James goes on to say you do well, or as Good News Translation has rendered it, “Good!” (so also New International Version). However, the reason for citing it here is to point out that intellectual belief in itself is not enough. Affirming that God is one without allowing it to influence your life and conduct is simply inadequate and unreal. It may be observed that the commendation of “Good!” sounds a bit ironical in view of what James goes on to say immediately, Even the demons believe [that]—and shudder. Another possible rendering for Good is “That’s fine!” (Contemporary English Version), which in English sounds more ironical. A person who believes in the oneness of God without allowing this belief to change his or her conduct shares this faith with the demons, the evil spirits. This is not the kind of faith that can save. In the New Testament the demons do express belief in the divine (Mark 1.24; 5.7; Acts 16.16-17); and in stories of exorcisms they show fear before Christ (Mark 1.23, 24; 5.7). In front of God, their arch enemy, the demons shudder: they “tremble with fear” (Good News Translation). In a number of languages it will be necessary to add the idea of “fear” to shudder to make clear for the reader why the demons tremble. Other ways to express this are “so afraid that they tremble all over” or “so afraid that their hearts tremble [or, quake].” Demons were thought of as evil spiritual beings (“evil spirits”) or “unclean spirits” under the control of the Devil.

Quoted with permission from Loh, I-Jin and Hatton, Howard A. A Handbook on The Letter from James. (UBS Handbook Series). New York: UBS, 1997. For this and other handbooks for translators see here .