Was the "redrum door" an inverted cross?
Here is the most famous shot of the "redrum door", although it only appears in the film for a few scant seconds:
https://external-preview.redd.it/ul4F2B1qnFPqfulNtv4cYwpzK4tu9eXmEwcGYtSGJKI.jpg?auto=webp&s=eabde5775f167099303d052b98b59a46d5fc9d7f
Notice how the paneling on the door forms an inverted cross. Is it a coincidence that "redrum" (a symbol for blood and wine?) just so happens to spell "murder" if inverted horizontally, and just so happens to be written on a door which when flipped vertically is a Christian Cross? Think also of the links between Christ's death on the cross, the symbolic importance of his blood and it's ritual association with wine.
The music used when Jack does his first killing is intercut with the "redrum door", the "blood elevators" and the music of Penderecki. https://www.youtube.com/watch?v=OChx37ef5zU&t=63s Is it really a coincidence that the rattling music used in that scene is an EASTER work, part two of Penderecki's Utrenja (depicting the Resurrection). This part is called entitled Part II: Zmartwychwstanie Pańskie (The Resurrection of Christ) I. Ewangelia (The Gospel). https://en.wikipedia.org/wiki/Utrenja. Notice how Jack "rises" into frame after killing Halloran and Penderecki rattling music from this piece is heard. The music is visually associated with both the door and the elevator.
One other thing, one shot in particular of the door is shot at a very striking and unusual angle. If you flip the door vertically, the angle of the door will remind you of a famous depiction of the Crucifixion by Salvador Dali, "Christ of St. John of the Cross":
https://en.wikipedia.org/wiki/Christ_of_Saint_John_of_the_Cross
This "St. John" crucifix appears in several other religious works by Dali, most notable his "The Discovery of America by Christopher Columbus". Notice the angle of the crucifix the priest is holding in the bottom center of the painting, and a second and larger one in the upper right third of the painting:
https://i.pinimg.com/originals/12/7c/02/127c02b861f6ace7546063262ce66d85.jpg