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.

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

479. And He that sitteth on the throne shall dwell over them, signifies the influx of Divine good into the truths with them. This is evident from the signification of "He that sitteth on the throne," as being the Lord in relation to Divine good (of which above, n. 297, 343, 460); also from the signification of "dwelling over them," as being to flow in with good into their truths; for "to dwell" is predicated in the Word of good, thus "dwellers" signify those who are in good; so when "to dwell" is predicated of the Lord, as here, "to dwell over them" signifies the influx of Divine good; this is into truths, because the truths in such are what have just been treated of, also because all who are in the heavens are held in truths by the influx into truths of Divine good from the Lord; for it is only into truths that Divine good can flow, because truths are from good, for they are forms of good; this is why it is necessary for man to be in good, since by it the Lord flows into the truths corresponding to the good.

He is much mistaken who supposes that the Lord flows immediately into truths with man. (This influx is treated of in the Arcana Coelestia, namely, the influx of the Lord is into the good with man, and through the good into the truths that are with him, but not the reverse, n. 5482, 5649, 6027, 8685, 8701, 10153; influx is through good into truths of every kind, but especially into genuine truths, n. 2531, 2554; in good there is a faculty of receiving truths, n. 8321; there is no influx of the Lord into truths separate from good, n. 1831, 1832, 3514, 3564.) From this it can now be seen how the things contained in this and the preceding verses cohere, namely, that those in whom truths from the Lord are implanted by means of temptations, are constantly held in truths by the influx into them of Divine good. (That "to dwell" is predicated in the Word of good, see Arcana Coelestia 2268, 2451, 2712, 3613, 8269, 8309, 10153; and that "the dwelling place of the Lord" means heaven and the church in respect to good, consequently the good of heaven and the church, and in reference to man the good with him, n. 8269, 8309)