Malory, Morte D’Arthur, Book 14.10 (290): Percival learns of the significance of his encounter with the mysterious lady

'O good knight,' said he. 'thou art a fool, for that gentlewoman was the master fiend of hell, the which hath power above all devils, and that was the old lady that thou sawest in thine advision riding on the serpent.'

Then he told Sir Percival how Our Lord Jesu Christ beat him out of heaven for his sin, the which was the most brightest angel of heaven, and therefore he lost his heritage: 'And that was the champion that thou foughtest withal, the which had overcome thee had not the grace of God been. Now beware Sir Percival, and take this for an example.'

The same scene from the Queste del Sant Graal (from Stephen H.A. Shepherd, ed., Le Morte Darthur [Norton, 2004]):

"The young woman you spoke to is the devil, the master of hell who has power over everyone. It is true that she was formerly in heaven, in the company of angels, beautiful and luminous. But the devil's great beauty made him proud and so eager to rival the Trinity that he said, 'I will ascend to heaven and become equal to the Good Lord.' As soon as he had said this, Our Lord, who did not want His house to be defiled by the poison of pride, made him fall from the high seat where He had placed him and sent him to the dark house known as hell. When he found himself cast down from the distinguished seat he had been occupying into everlasting darkness, he decided to wage an all-out war against the one who had put him there. But he did not know exactly how. Finally, he became acquainted with Adam's wife, the first woman of the human race. He watched her and trapped her into committing the same mortal sin that had caused his expulsion from the glorious heavens: the sin of covetousness. Encouraging her treasonous impulses, he led her to pick the deadly fruit from the tree that God’s own voice had prohibited. When she had picked it, she ate of the fruit and gave some to her husband Adam to eat, with the result that all their descendants have felt the mortal effect of this act. The devil, who advised Eve to do this, was the serpent that you saw the old woman riding the day before yesterday; it was also the young woman who paid you a visit last night. When she explained that she was fighting day and night, she spoke the truth, as you well know. She never ceases to stalk the knights of Jesus Christ, all worthy men and servants in whom the Holy Spirit resides.

"Once she had appeased you with her false words and cunning, she had the tent set up to protect you and said, 'Come and rest here, Perceval; sit here until nightfall. Move out of the sun; I have a feeling that you are getting too hot.' The words she spoke are not without great significance. She took them to mean something very different from what you understood. The tent, which was round like the circumference of the earth, clearly represents the world, which will never be without sin. It is because sin always resides therein that she did not want you to remain outside the tent; indeed, that is why she had it set up for you. When she called to you, she said, 'Perceval, come and rest here; sit here until nightfall.' By this she meant that you should be idle and nourish your body in gluttony with earthly foods. She did not encourage you to work in this world or sow seeds that wise men could harvest on Judgment Day. She asked you to rest until nightfall, that is to say, until death overtook you. Indeed death is called night whenever it overtakes a man caught in mortal sin. She called to you because she thought the sun was heating you up too much. It is not surprising that she would fear that. When the sun, by which we understand Jesus Christ, the true light, warms the sinner with the fire of the Holy Spirit, the cold and ice of the devil can to little to harm him, provided he has fixed his heart on the lofty sun. I have spoken about this lady long enough to let you know who she is and how her visit would have harmed rather than helped you."