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.

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

664. Verse 11. And after the three days and a half, signifies when it is finished, thus the end of the old church and the beginning of the New Church. This is evident from the signification of "the three days and a half," as being fullness and completion as to the end of the old church, when there is the beginning of the New Church (See above, n. 658). It is said "after the three days and a half" because in the Word "days" signify states, here the last state of the church; for in the Word all times, as "hours," "days," "weeks," "months," "years," "ages," signify states, as here the last state of the church, when there is no longer any good of love or truth of faith left. Because "days" signify states, and the establishment of the Most Ancient Church is treated of in the first chapter of Genesis, and it becomes established successively from one state to another, it is there said:

That there was evening and there was morning the first day, the second, the third, the fourth, the fifth, and the sixth days, even to the seventh, when it was finished (Genesis 1:5, 8, 13, 19, 23, 31; 2:2);

and the "days" there do not mean days, but the successive states of the regeneration of men at that time, and the consequent establishment of the church with them. So also elsewhere in the Word.