The Moxen are some knights. I guess they might be important.
Shael discovered that the Moxen were an order of knights in ancient Thran. The gems were utilized by the powerful society to draw power off of the Weapons, which were massive but natural engines of destruction, created by the world of Terra itself. Threats to the planet were met by the weapons, which tended to obliterate them. They were not subtle devices, and entire cities or peoples might be wiped out when their power was unleashed. The Sapphire Mox he wields is linked to the Sapphire Weapon, a colossal sea creature with dozens of tentacles. As the Weapon comes from the deepest parts of the ocean, he is able to withstand and utilize chilling forces to heal his own body. This power is effectively infinite, given the mighty creature it siphons from, though extreme use over a short period of time might be enough to cause the Weapon to stir.
The Moxen were ultimately intended as suicide sacrifices, should their Weapon awake and threaten Thran, the knight was to activate his gem and lead the Weapon away. If the knight was unable to find a way to put the Weapon back to sleep, the Mox gem was enchanted so that dealing a death blow to the attuned knight would absorb its energy and send it back into stasis. This would also render the knight truly dead, beyond even the power of the gods themselves to restore. Such was their responsibility.
The Mox Sapphire functions as an amulet of protection and ring of cold resistance. Once per short rest, the wearer can cast an illusion or divination spell and cause the target to suffer disadvantage on their save. When worn by the actual Sapphire Knight, the Mox absorbs cold damage and heals the wearer a like amount