Just as a whole community is a heaven in lesser form, so too an angel is a heaven in least form. For heaven is not outside angels but within them. Their deeper levels, the levels of their minds, are arranged in the form of heaven and therefore are arranged to accept all the elements of heaven that are outside them. These elements they accept according to the quality of the goodness that is within them from the Lord. As a result, an angel is also a heaven.
It can never be said that heaven is outside anyone. It is within; because every angel accepts the heaven that is outside in keeping with the heaven that is within. We can see, then, how mistaken people are who think that getting into heaven is simply a matter of being taken up among the angels, regardless of the quality of their inner life, who believe that heaven is granted merely because of [the Lord’s] mercy. On the contrary, unless heaven is within an individual, nothing of the heaven that is outside flows in and is accepted.
There are many spirits who hold this opinion and who, because of their faith, have been taken up into heaven. However, once they arrived, because their inner life was contrary to the life angels are engaged in, they began to be blinded in their understanding to the point that they became virtually idiotic, while in regard to their self-control they began to be so tormented that they carried on like people gone mad. In short, people who have lived evil lives and who arrive in heaven bring their souls with them and are tormented like fish out of water, in the air, or like animals in the vacuum in air pumps once the air has been pumped out. It stands to reason, then, that heaven is within us and not outside.
Since everyone accepts the heaven that is outside according to the quality of the heaven that is within, angels accept the Lord in the same way, because it is the Lord’s divine nature that constitutes heaven. Consequently, when the Lord renders himself present in any particular community, his appearance depends on the nature of the good activity that community is engaged in. It is therefore not exactly the same in one community as in another. It is not that this difference is in the Lord: it is in the individuals who are seeing him from their own goodness and therefore in keeping with it. They are affected by the sight of him according to the quality of their own love. The ones who love him deeply are deeply moved, while the ones who love him less deeply are less deeply moved. Evil people, who are outside of heaven, find his presence intensely painful.
When the Lord does appear in any community, he appears there as an angel, but he is identified by the divine quality that shines through.
from Heaven and Hell, Sections 53-55