The Monk is one of the more lurid and "transgressive" of Gothic novels. It is also the first book to feature a priest as the villain. In this respect it would serve as a model for such future works of literature as The Hunchback of Notre Dame.
This novel shares a number of traits with Ann Radcliffe's gothic novels The Italian and The Mysteries of Udolpho.
Featuring demonic pacts, rape, incest, and such props as the Wandering Jew, ruined castles, and the Spanish Inquisition, The Monk serves more or less as a compendium of Gothic taste. Ambrosio, the hypocrite foiled by his own lust, and his sexual misconduct inside the walls of convents and monasteries, is a vividly portrayed villain, as well as an embodiment of much of the traditional English mistrust of Roman Catholicism, with its intrusive confessional, its political and religious authoritarianism, and its cloistered lifestyles. The American fictitious anti-Catholic libel, The Awful Disclosures of Maria Monk, borrowed much from the plot of this novel. Despite the critics' comments on its crudeness and lack of depth, it proved to be one of the most popular novels of the Romantic Period.
It is among the many Gothic works referenced in the Jane Austen novel Northanger Abbey.
This novel was considered by the Marquis de Sade as a reaction to the 1789 French Revolution, with Lewis using the Gothic to express concerns circulating around England in the Romantic Period. Concerns such as social stability and the mis-use of power are some of the issues explored.
Robert Miles suggests that The Monk is about “veiling and disguise”  and that it is possible to read into the novel a possible expression of the “open secret” of Lewis’s homosexuality through the characters of Ambrosio, Rosario/Matilda, and Lucifer. “In the end, Ambrosio’s desires are insatiable... But Ambrosio’s desire may be insatiable because it is denied its true object. The closest the text gets to disclosing what this object might be is an elaborately staged event which obfuscates as it reveals. In the centre of the text, in quick succession, Matilda performs two acts of conjuration. In the first, Antonia’s coy, modest, naked body is displayed before Ambrosio in Matilda’s magic mirror. In the second, in labyrinthine caverns beneath the monastery, Matilda invokes an androgynous, decidedly camp ‘Daemon’: ‘a Youth seemingly scarce eighteen, the perfection of whose form and face was unrivalled’. The ‘beautiful’ figure, ‘perfectly naked’, with ‘silken locks’ and surrounded by ‘clouds of rose-coloured lights’ (277), appears as the key to Ambrosio’s possession of Antonia. The figure, at Matilda’s strident behest finally relinquishes the 'myrtle' which will enable Antonia’s seduction. The parallelism of the staging raises the question of causation: is the Daemon the key to the sexual possession of Antonia, or is Antonia’s image a screen for Ambrosio’s true object of desire, the epicene devil?”
The Wandering Jew and the Bleeding Nun
The Wandering Jew is a man doomed to walk the earth until the second coming of Jesus. There are several interpretations of why he is punished this way. One legend says that Jesus wished to take a drink from a horse trough and the Jew refused, instead pointing to a hoofprint filled with water on the ground and “observed that it was good enough for such an enemy of Moses”. Another legend says that when Christ sat to rest on a man’s doorstep, a man from Jerusalem drove him away, yelling, “‘Walk faster!’ And Christ replied, ‘I go, but you will walk until I come again!’”  Both these legends show that the Jew’s rude behavior to Christ is the reason for his punishment of endless wandering.
The Wandering Jew appears in the subplot of Raymond and Agnes’ story in The Monk and foreshadows Ambrosio’s encounters with supernatural devilish spirits. The Wandering Jew is first referenced to as a “Great Mogul,” but he displays several characteristics associated with the legend of the Wandering Jew that allow us to figure out his true identity before it is directly revealed. He tells Raymond:
- Fate obliges me to be constantly in movement; I am not permitted to pass more than a fortnight in the same place. I have no friend in the world, and, from the restlessness of my destiny, I never can acquire one. Fain would I lay down my miserable life, for I envy those who enjoy the quiet of the grave; but death eludes me, and flies from my embrace.
This speech reveals that this Great Mogul must constantly move from place to place, has no friends, and can never die. All of these signs point to the legend of the Wandering Jew. On top of this, the Great Mogul reveals, “God has set his seal upon me, and all his creatures respect this fatal mark”. This refers to the burning cross on his forehead, a mark of God that gives the Great Mogul his power to destroy evil spirits, such as the Bleeding Nun. This burning mark is a characteristic of the Wandering Jew specifically found in Spanish variants of the legend. The Monk is primarily set in Spain and its main characters, like Raymond, are mostly Spanish. Therefore, the Wandering Jew fulfills the aspects of the legend most commonly found in Spain. Another characteristic of the Wandering Jew found in Spain is that although he is miserable and cursed, he spends his time praying, doing good works, and helping others. Theodore tells Raymond that “he did much good in the town,” and he helps Raymond get rid of the Bleeding Nun. The Great Mogul’s identity as the Wandering Jew is eventually revealed:
- When I [Raymond] related my adventure to my Uncle, the Cardinal-Duke, He told me that He had no doubt of this singular Man’s being the celebrated Character known universally by the name of ‘the wandering Jew.’ His not being permitted to pass more than fourteen days on the same spot, the burning Cross impressed upon his fore-head, the effect which it produced upon the Beholders, and many other circumstances give this supposition the colour of truth.
The Cardinal-Duke’s confirmation and belief in the existence of the Wandering Jew gives credit to Raymond’s story.
The Bleeding Nun also appears in the subplot of Raymond and Agnes and epitomizes the sin of erotic desires. Raymond mistakes her for his lover, Agnes, because she is veiled and he cannot see her face. The veil “conceals and inhibits sexuality comes by the same gesture to represent it.” Both Antonia and Matilda are veiled to protect their virginity and innocence and it is expected that Agnes also covers her face for this reason when she meets Raymond. However, the removal of the veil reveals the Bleeding Nun, dead and punished because of her sins. While she was alive, she was a prostitute and a murderer before she was murdered by her lover. Her story is the first we receive of how giving in to sexual desires leads to death and eternal unrest. Raymond expects to find Agnes’ beautiful, virgin face beneath the veil, but instead finds death. Her unveiling connects the loss of virginity and the giving in to sexual desires with death and punishment. Both the Bleeding Nun and Ambrosio begin pious but then fall prey to their sexual desires. Ambrosio has already given into his desire for Matilda and the story of the Bleeding Nun told in the subplot foreshadows his further downfall with Antonia and his eternal punishment in the hands of the devil.
The Bleeding Nun also introduces the world of the supernatural into The Monk. The supernatural something “that is above nature or belonging to a higher realm or system than that of nature”  This introduction brings another Gothic element into the book. Up until this point, the plot has relied on natural elements of the sublime to invoke the terror expected of a Gothic novel. The entrance of the Bleeding Nun transforms this natural world into a world where the supernatural is possible. When she gets into Raymond’s carriage, “Immediately thick clouds obscured the sky: The winds howled around us, the lightning flashed, and the Thunder roared tremendously.” Nature is acknowledging the presence of a supernatural force.
When Agnes tells Raymond the story of how the Bleeding Nun’s ghost haunts the Castle of Lindenberg, Raymond asks her whether she believes the story, and she replies “How can you ask such a question? No, no, Alphonso! I have too much reason to lament superstition’s influence to be its Victim myself.” It is not until the Bleeding Nun appears to Raymond at night that the idea of the existence of the supernatural begins to be a reality. The Wandering Jew’s appearance coincides with this first instance of the supernatural. He can see the Bleeding Nun, proving that she is not a figment of Raymond’s imagination. His supernatural abilities give access to the Bleeding Nun’s story and provide plausibility to the existence of the supernatural. He also has the power to free Raymond from her presence. The later confirmation of Raymond’s uncle to the existence of the Wandering Jew allows the whole story to be taken for fact. This establishes the reality of the supernatural and lays the groundwork for Matilda’s later use of magic and her and Ambrosio’s interaction with evil spirits.