Actual heavenly joy as it is in and of itself is beyond description because it dwells in the deepest natures of angels. It flows from there into the details of their thought and affection and from these into the details of their speech and action. It is as though their deeper levels were wide open and freed to accept a delight and bliss that spreads out through all their fibers and therefore through their whole being, giving them a kind of perception and feeling that simply cannot be described. Anything that arises from the deepest levels flows into the details that derive from those deepest levels and proliferates toward the outer levels, constantly gaining strength.
When good spirits who have not yet experienced this pleasure (not having been raised into heaven yet) perceive it from the aura of love from some angel, they are filled with such pleasure that they find themselves in a kind of sweet faint. This often happens to people who want to know what heavenly joy is.
from Heaven and Hell, Section 409