But when the souls of those who die for the Christian faith depart from the body with great glory, they destroy the power of the demons, and frustrate their designs against men. Wherefore I imagine, that as the demons have learned from experience that they are defeated and overpowered by the martyrs for the truth, they are afraid to have recourse again to violence. And thus, until they forget the defeats they have sustained, it is probable that the world will be at peace with the Christians.
But when they recover their power, and, with eyes blinded by sin, wish again to take their revenge on Christians, and persecute them, then again they will be defeated, and then again the souls of the godly, who lay down their lives for the cause of godliness, shall utterly destroy the army of the wicked one. And as the demons perceive that those who meet death victoriously for the sake of religion destroy their authority, while those who give way under their sufferings, and deny the faith, come under their power, I imagine that at times they feel a deep interest in Christians when on their trial, and keenly strive to gain them over to their side, feeling as they do that their confession is torture to them, and their denial is a relief and encouragement to them.
And traces of the same feeling may be seen in the demeanour of the judges; for they are greatly distressed at seeing those who bear outrage and torture with patience, but are greatly elated when a Christian gives way under it. Yet it is from no feeling of humanity that this arises. They see well, that, while “the tongues” of those who are overpowered by the tortures “may take the oath, the mind has not sworn.” And this may serve as an answer to the remark of Celsus: “But they severely punish one who reviles them, so that he must either flee and hide himself, or be taken and perish.” If a Christian ever flees away, it is not from fear, but in obedience to the command of his Master, that so he may preserve himself, and employ his strength for the benefit of others.
Source: Against Celsus (New Advent)