Midst
The "midst" of something in the Bible represents the thing that is most central and most important to the spiritual state being described, the motivation that drives everything else. In general this will be something we love or feel, because at the core of things we are what we love; our loves define us.
(Reference: Apocalypse Revealed 44, 90, 268; Arcana Coelestia 2252, 2940, 10153, 10365, 10557, 10635, 10641)
Heaven and Hell #116
116. The Sun in Heaven
Our world's sun is not visible in heaven, and neither is anything that is derived from it, since all that is natural. Nature, in fact, begins with that sun, and whatever is produced by it is called natural. The spiritual reality in which heaven exists, though, is above nature and completely distinct from anything natural. They communicate with each other only through correspondences.
The nature of the distinction can be gathered from what was said above about levels in 38, and the nature of the communication from the last two chapters about correspondences.