"Introibo ad altare Dei": Mulligan’s first words initiate a mocking parody of the Catholic Mass, though in retrospect the stage has been set by his “stately” appearance carrying a bowl on which a mirror and razor lie “crossed.” In his mock ritual, the shaving bowl represents the chalice (or ciborium, or pyx) that holds the wine which will become changed into the blood of Christ. The Latin phrase means “I will go up to the altar of God.”
The words are taken from Psalm 43 (42 in the Vulgate), which expresses a desire to find refuge in God. In the days of the Latin Mass (pre-1964) it was chanted by the celebrant as he prepared to ascend the steps of the altar. The first two of the following three video clips show priests and their servers approaching the altar in an Irish and a Polish church. The third video presents a skilled Italian chanter singing the Introibo.
Gifford observes that the server assisting the celebrant of the Mass responds to his Introibo by quoting from the next line of the Psalm: Ad Deum qui laetificat juventutem meam, “To God who gladdens my youth.” When Father Malachi O'Flynn celebrates an even more diabolic black mass in Circe by singing "Introibo ad altare diaboli," his server perverts the responsory line too: "To the devil which hath made glad my young days."
Stephen, who thinks of himself later in Telemachus as a server (and thus a servant) to Mulligan, does not speak the line responsorially to Mulligan’s Introibo, but he too speaks it in a twisted way in Circe, as he approaches the brothel where he hopes to meet his favorite prostitute: “Georgina Johnson, ad deam qui laetificat iuventutem meam.” By making Georgina into a goddess (deam), Stephen perverts the language of the Mass just as Mulligan does with his "genuine Christine," and insinuates the serious thought that, in this secular world, human sexual love fulfills a need which medieval men and women turned to God to satisfy.
The two men differ greatly in their attitudes toward religious mystery. To Mulligan it is mere humbug. For Stephen, the rites of the Catholic Church deserve respect and even veneration, as forms of spiritual apprehension that literary art may learn from. Like Joyce in his twenties, he recurs often to religious metaphors to express what he wants to do in his art. One of these powerful religious symbols is the transubstantiation effected in the Mass. In the final section of A Portrait, after renouncing his religious vocation and choosing the life of an artist, he thinks of himself as “a priest of eternal imagination, transmuting the daily bread of experience into the radiant body of eternal life”—a function that surpasses the actions of a parish priest, “one who was but schooled in the discharging of a formal rite” (240). Later in Telemachus, it will become apparent that Stephen despises Mulligan’s mocking attitude toward religious faith, even though Stephen himself is an apostate, bitterly determined to "kill the priest and the king" and free himself from subjection.
The mock Mass may have yet another function in the opening of Ulysses. Gifford plausibly suggests that, since the Homeric epics begin with an invocation of the poetic Muse, Mulligan’s “intoned” words do not only mock religion. They also suggest that this will be a mock-epic. When the book was first published, its title spurred debate about whether its adventures should be seen only as a mockingly debased version of great Greek antecedents, or as a more serious instantiation of Homeric patterns. To some degree that uncertainty still continues, as do questions about how extensive and significant the book’s Homeric parallels may be. Joyce’s parodic relation to his elevated epic source, and to the religion of his youth, is deeply ambiguous—at once respectful and irreverent, preservative and transformative.