It is unknown how the wall was created and what it's origins are. It was discovered by Izaya on a long walk of self discovery he
took to purge himself of the evil influence of Darkseid
. When he started to question his beliefs and his purpose, he suddenly came across a plain looking slab of unknown material. In rage, he struck the slab with his power, and the Source
revealed itself to him. At that point Izaya denounced his warrior ways, instead becoming a leader full of peace and understanding. Becoming the Highfather.
The wall was removed from the wasteland where it was found and brought to the chamber of the Source in the Celestial City
to become the city's holiest object, an, indeed, the holiest object on all New Genesis
The Source manifests itself as a flaming hand writing prophetic and often cryptic messages on the wall. It has guided the Highfather through his long reign, and after he passed away, it has guided Takion
in the same way.
It is presumed that the Wall of prophecy was destroyed in Darkseid's attack on New Genesis. The wall has manifested itself on Earth several times, proving that the wall itself was merely a simple conduit for the wisdom of the Eternal Source.