We may also gather how vast the Lord’s heaven is from the fact that heaven in a single complex resembles a single human being and also corresponds to everything within us. This relationship can never be completely filled in because there is a correspondence not only with the particular members and organs and viscera of the body but also, in most minute detail, with all the tiny organelles and viscera within them, even with the individual vessels and fibers—and not only with these, but with the organic substances that receive the inflow of heaven from within, the inflow that gives us the inner processes that support the workings of our spirits. In fact, everything that happens within us happens in the forms of our substance; anything that does not happen in substances as agents is nothing. There is a correspondence of all these substances with heaven, as you may gather from the chapter on the correspondence of everything in heaven with everything in the human being (Sections 87–102). This correspondence can never be completely filled in because the more assemblies of angels there are that answer to each member, the more complete heaven is. In the heavens, all forms of perfection increase as numbers increase. This is because there is one goal for everything there and a unanimous focus of everyone on that goal. That goal is the common good; and when this rules, there is benefit to individuals from the common good and from the good of individuals to the good of the whole. This happens because the Lord turns everyone in heaven toward himself (see above, Section 123) and in this way makes them one with himself.
Anyone with a little rational enlightenment can figure out that the unanimous harmony of many people, especially from such a source and with such intimacy, brings forth perfection.
I have been allowed to see the extent of the inhabited heaven and also the extent of the uninhabited heaven; and I have seen that the uninhabited heaven is so vast that it could never be filled to all eternity even if there were thousands of thousands of planets with as many people on each one as there are on ours.
from Heaven and Hell, Sections 418, 419