Legion-4 was selected to reincarnate as a giant of order because of their unique power. Gehaldirah had done some research on them and confirmed the common knowledge that their power is due to their divine ability being related to the law of order.
The law of order is a very unique law that is almost impossible to learn. It is very rare to come across like the law of chaos, because anything that comes close to order gets overwritten. That's why spells that come close to a giant of order get unraveled into their basic form of mana.
The law of order is very important for an Origin god to become a world god but it can't be comprehended. Instead, it is created. Since Origin gods can't learn it, they create a substitute for it using the other laws that they have learned. It may be artificial but it is under their control.
I've started a new book titled DESTINY GAMES. Please check it