The letter mentioned many things that were beyond Gabriel's comprehension. It talked about an entire civilization that was beyond his wildest imaginations.
It was a civilization of beings that were true immortals. They couldn't be killed, no matter what. Even the strongest attack in the world couldn't leave the lightest scratch on their body.
It was so unimaginable that Gabriel even wondered if Ezekiel was joking with him, just for him. This civilization was stronger than even the Ancient Gods that he had read about. However, there was one thing that was different about them.
While the Gods could have an infinite lifespan until they were killed or they intentionally went to Eternal sleep, the beings of this unknown civilization had a lifespan of only two hundred years only.