[T]he demons can only do superficially, that is, under the force and great compulsion of God’s almighty power. But they cannot do these things interiorly, that is, voluntarily and willfully, by the consent of their free will. Wherefore, even if they say that they believe: “Even the demons,” says James the Brother of God, “believe and shudder” (Jas. 2:19), their faith is not an unhesitating consent to the commands of God, as Basil the Great defines faith. And even if they confess the truth, and even if it seems from some outward appearances that they rejoice, or that they submit to God, all these things are done by compulsion, and by force, without the consent of their free will.
Let us explain this more clearly. Even if the demons outwardly appear to believe, they are inwardly faithless. Even if they outwardly appear to confess the truth, they inwardly reject it and lie. Even if they outwardly appear to be rejoicing, they are inwardly grieving. Even if they outwardly appear to be submissive and obedient, they are inwardly insubordinate and disobedient. Even if they outwardly appear to be conquered and humbled, they inwardly are prideful. It follows, then, that faith is not counted as righteousness unto them, because it is forced and unwanted… [N]either does their involuntary confession of the truth, nor their compelled joy and submissiveness profit them at all or assist them in salvation. But neither are the things which demons say virtues at all, not having been chosen by them. For that which is compelled and forced is not virtue… There is nothing worse than the misery of demons. (Confession of Faith, 5: Concerning the Story of the Magi)