However, people who live in the same heaven can associate with anyone there, and their delight in getting together is in proportion to the similarity of the values they are devoted to. There will be more about this, though, in later chapters.
Even though the heavens are so distinct from each other that angels of one heaven cannot have regular dealings with angels of another, still the Lord unites all the heavens by means of a direct and an indirect inflow. The direct inflow is from him into all the heavens, and the indirect is through one heaven into another. In this way, the Lord brings about a unity of the three heavens. They are all linked together, from the First to the last, so that nothing exists that is not connected. Anything that is not connected to the First by some intermediary does not endure, but disintegrates and becomes nothing.
from Heaven and Hell, sections 36, 37