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In the ancient and medieval worlds, androgynous people and/or hermaphrodites were represented in art by the caduceus (staff and intertwined snakes), a wand of transformative power in ancient Greco-Roman mythology (compare also DNA double-helix). The caduceus was created by Tiresias (blind prophet of Apollo in Thebes) and represents his transformation into a woman by Juno in punishment for striking at mating snakes. The caduceus was later carried by Hermes/Mercury and was the basis for the astronomical symbol for the planet Mercury and the botanical sign for hermaphrodite. That sign is now sometimes used for transgender people.
The satanists worship the merging or genders, or at least the expression of the "divine masculine" and the "divine feminine" in one body.
The cross (or saltire) is another ancient expression of the divine masculine. Combined with the circle of the divine feminine it becomes another representation of this androgynous transformation.
The satanists are all about transformation, from this human form which most of us rather like, to something totally new and inhuman. The satanists think this new form would be better.
Q asks us, What is the significance of the colors, design and symbol above the dome? Could Q be referring in part to the spire, which is another ancient symbol of the divine masculine (phallus) combined with the divine feminine (dome)? (Multiple answers to Q's question, I'm certain.)
A bit of research into the ancient history of the divine masculine and divine feminine also leads to historical research of "androgynous" individuals in ancient tribal cultures, who were regarded as having unique spiritual connections. Like the berdache shamans in early American Indian culture.
One theory: this satanic desire to merge both genders in one human being (androgyny, neutered, transgendered) is another plan to destroy us and alter us to become something else. In which case, the ancient tribal cultures were already compromised by satanic beliefs. The satanic religion seems to be the (second) oldest religion on the planet, which makes this a distinct possibility. In which case, who or what are the satanists emulating in their idealized design?
Another theory: this satanic desire to merge both genders in one human being somehow exploits some spiritual truth about the universe, that the ancient tribes also understood, that God made us all unique and there is some spiritual frequency more accessible to the androgynous. This might make gay people a particular threat to the satanic cult.
Theory three: both of the above theories might be true in combination.
Theory four: neither theory is true and that it's still something else entirely.