Do what thou wilt shall be the whole of the Law.
My own understanding of the Office of the Anthem in the Gnostic Mass has changed over time, and with the course of initiation. The Liber XV Anthem text is in some sense the kernel from which the Gnostic Mass was germinated. In his Confessions (p. 714), Crowley writes:
During this period [1913 e.v.] the full interpretation of the central mystery of freemasonry became clear in consciousness, and I expressed it in dramatic form in 'The Ship'. The lyrical climax is in some respects my supreme achievement in invocation; in fact, the chorus beginning:Thou who art I beyond all I am...seemed to me worthy to be introduced as the anthem into the Ritual of the Gnostic Catholic Church which, later in the year, I prepared for the use of the O.T.O., the central ceremony of its public and private celebration.
Crowley often referred to that invocation as the Tu Qui Es ("Thou who art"), and he referenced it as a component in his "Grimorium Sanctissimum"--his most powerful private ritual, incorporating both A\A\ and O.T.O. techniques in a single idiosyncratic canon.
The "priest's part" of the Tu Qui Es has two different versions. Some editions give: "Appear most awful and most mild, / As it is lawful, to thy child!" Others give "...in thy child!" (The sequence of editions suggests that Crowley started with "to" in The Ship, changed to "in" in early editions of the Mass, and eventually reverted to "to.")
Who or what is the entity invoked, the "Thou" addressed? Perhaps it is a function shared by every individual personal genius or holy guardian angel; perhaps it is the genius of humanity as a whole; perhaps it is the "carrier signal" of phenomenal reality. It seems to be an ultimate One, penultimate to the None. Is it the "particle of dust" which the priest "gives"? Is it the particula from the host that is the "seed" (SPERMA) of the priest? Is it the Lord of the Aeon, Ra-Hoor-Khuit? Is it Baphomet? Lucifer? Demeter? Jehovah? Satan? Osiris? Jesus? I assert none of these things, but I consider them all.
I would not rebuke a Thelemic Gnostic for choosing among them, or for rejecting them all. There is no formal doctrine explaining this mystery to the People of our Church; and in any case, our doctrines (e.g. the Creed) are those profound ideas that we must think about, not pre-fabricated notions to which we must conform without reflection.
Who is the child, within whom or to whom the invoked "Thou" is to appear? Perhaps that "Thou" is to appear within the Priest himself, appearing to the Priestess. Perhaps vice versa, or both reciprocally. Perhaps it is to appear in the graal after the commixto of the particula and the wine. Perhaps the child is the congregation, the Church as a whole, or humanity, or the Terrestrial System, or the Solar System, or the Galactic System. I assert none of these things, but I consider them all.
This sort of indeterminacy provides genuine catholicity in the ritual. The Roman church at its ritual best can include this sort of well-formed, yet unassigned sanctity. Particularly in the days of the Latin Mass, it has been impossible to know, on the basis of affiliation and attendance, whether a Roman devotee was principally worshipping Jesus, Jehovah, Mary, some saint or other, personal ancestors, or what have you. The mechanism of metaphysical ambiguity permits different individuals to approach the ceremony in their own spiritual perspective, and allows passage to other perspectives as well.
On the other hand, it is not helpful for a ritual officer to be wondering about such indeterminacy during the ceremony. An unresolved intellectual preoccupation is an obstacle to ritual puissance. In order to be reconciled to the work while enacting it, it is necessary either to make a provisional choice, or to permit a void to open within the question, so that there is "no difference" between the alternatives.
A provisional choice would impose a temporary resolution, in order to facilitate the work, with the idea that the ritualist could then evaluate the choice based on the results. ("Today, I'm going to direct the anthem to Eros. Let's see how that goes.")
In one sense, finding the void within the question suggests that the indeterminate object of the anthem is not essential to its function of adoration, so the ritualist could simply "let go" of that conundrum. A more elaborate way of finding the void would be to perform a synthesis on all of the objects considered feasible, so that the ritualist comes to understand, e.g. Jesus, Hadit, Satan, human sperm, and the axial orientation of the Solar System all as different perspectives on the same essence.
In addition to these considerations, the functional components of the Mass look very different from the various ritual roles of congregant, acolyte, deacon, priest, and priestess. A deacon, for example, might consider the Anthem to be a point at which the congregation is brought to identify with the priest, in preparation for the Mystic Marriage. A priestess, on the other hand, might see it as a stage in which she aligns subtle currents in herself and the priest. A priest might look at it as a period of "ripening" in which the charged elements of the eucharist grow ready for consummation.
Cardinal Sacraments: The Eucharist of the Gnostic Mass
Vigorous Food & Divine Madness