Abel's Ark and U-DO Edit
The Galaxy Federation perceives it to be a giant Gnosis; however, it is actually one of the "eyes of U-DO"; U-DO's observational terminal in this dimension (along with Abel, U-DO's human form). According to the Episode III database, it has the power to change its perceived shape based on circumstances, and it only serves as an observer.
It is the form of Abel's consciousness manifested in real space (similar to the Testaments). The real space and the imaginary space are two planes of existence interwoven with each other in the Xenosaga universe. Real space is the plane of existence consisting of physical being and flesh, while imaginary space consists of consciousness. As the Ark is from the Imaginary Domain, it does not exist physically. Abel's Ark is the form of Abel's consciousness while Abel is the form of U-DO's physical being. They are referred to as "U-DO's eyes" because U-DO exists outside of the universe (the "Upper Domain"). Abel's Ark and Abel are the way those within our universe (the "Lower Domain") perceive U-DO's observation.
Its primary shape resembles a crystalline tree or chandelier. The database claims that the ringed object in the center of its structure is not a planet, but an energy field.
Xenosaga Episode II: Jenseits von Gut und Böse Edit
After the space-time anomaly collapses, Abel's Ark appears out of nowhere and swallows the Zohar in space and then disappears.
Xenosaga Episode III: Also sprach Zarathustra Edit
In Shion Uzuki's subconscious ("Miltia"), Abel's Ark was summoned during the Miltian Conflict when Shion's despair, caused by the deaths of her parents Suou and Aoi, resonated with the Zohar in Labyrinthos. This is because the Zohar is a portal to U-DO, and Shion was really resonating with U-DO. The awakening of U-DO was responsible for the summoning of Abel's Ark.
Abel's Ark is later explored as a dungeon.
In the ending, Abel's Ark reconfigures into a shape resembling a cross, possibly a reference to the crucifix Jesus was supposedly crucified on. It appears to have a cleansing effect, wiping out the Gnosis surrounding Michtam, possibly symbolizing Jesus wiping out humanity's sins.
Episode III database Edit
A perceptual phenomenon that is the lower-dimensional, tangible form of the (imaginary-space) consciousness of the higher-dimensional being U-DO (Abel). It is a perceptual phenomenon in the same way that the Gnosis are, but it is also a completely different form of existence.
Abel's Ark (U-DO) observed Albedo's consciousness during the fall of Old Miltia. It later took in the Zohar as a connection point in order to more steadily observe the lower dimension.
After Shion's awakening, the Ark's imaginary-space transformation accelerated, reflecting the consciousness of mankind. Detecting the operation of Zarathustra, an anti-higher-dimensional system constructed ages ago, it took the planet Michtam into itself. This action was not taken in an attempt to destroy Zarathustra; it was purely trying to "observe" the changes in the consciousness of the lower dimension.