To the extent that truths of the intellect are united to good things of the will, then, or to the extent that we intend and therefore do truths, we have heaven within us, because as already noted the union of the good and the true is heaven. However, to the extent that false elements of intellect are united to evil elements of will, we have hell within us, because the union of the false and the evil is hell. Still, to the extent that truths of intellect are not united to good elements of will, we are in the halfway state. Almost all of us nowadays are in a state in which we know things that are true and think about them on the basis of our information and also from our intellect.
We act on either a lot of them or a few of them or none of them or act contrary to them because of our love of evil and consequent trust in what is false. So in order that we may gain either heaven or hell, after death we are first taken to the world of spirits, where either the union of the good and the true takes place for people who are to be raised into heaven, or the union of the evil and the false for people who are to be cast into hell. This is because no one in heaven or in hell is allowed to have a divided mind, to understand one thing and intend something else.
What we intend we understand and what we understand we intend. Consequently, anyone in heaven who intends what is good understands what is true, and anyone in hell who intends what is evil understands what is false. So for good people, the false elements are taken away and they are given truths suited and fitted to their virtue, while for evil people truths are taken away and they are given false elements suited and fitted to their vice. This enables us to see what the world of spirits is.
from Heaven and Hell, Section 425