Since there are infinite varieties in Heaven–since no community and in fact no individual is just like any other–heaven is therefore divided overall, more specifically, and in detail. Overall, it is divided into two kingdoms, more specifically into three heaves, and in detail into countless communities. We will now discuss the details. They are called “kingdoms” because heaven is called “the kingdom of God.”
There are angels who accept the divine nature that emanates from the Lord on a deeper level and angels who accept it less deeply. The ones who accept it more deeply are called heavenly angels, and the ones who accept it less deeply are called spiritual angels. Heaven is therefore divided into two kingdoms, one called the heavenly kingdom and the other called the spiritual kingdom.
from Heaven and Hell, Sections 20, 21