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.

(Odkazy: Apocalypse Revealed 44, 90, 268; Arcana Coelestia 2252, 2940, 10153, 10365, 10557, 10635, 10641)

647. It is bound to seem strange and very far-fetched to everybody that these details have this meaning, that is to say, that the numbers three hundred, fifty, and thirty mean remnants, and in particular that they were few; also that 'length, breadth, and height' means holiness, truth, and good. But in addition to what has been stated and shown above about numbers at verse 3 of this chapter, where a hundred and twenty means the remnants of faith, this matter may also become clear to anybody from the fact that people who possess the internal sense, as good spirits and angels do, are beyond anything earthly, bodily, or purely worldly, and so beyond anything involving numbers and measurements. Yet the Lord enables them to perceive the Word fully, and to do so quite independently from such concepts. This being so, it becomes quite clear that numbers and measurements embody celestial and spiritual things. The latter however are so remote from the sense of the letter that such things cannot possibly be seen. This applies to every single celestial or spiritual thing. From this also anyone may recognize how insane it is to desire to inquire into matters of faith through sensory evidence and factual knowledge and to refuse to believe unless one grasps them by that method.