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.

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

268. And I looked, and behold, in the midst of the throne and of the four living creatures, and in the midst of the elders. (5:6) This symbolically means from the inmost elements of heaven, the Word, and the church, and so in all their constituents.

"In the midst" means, symbolically, in inmost elements and so in all (no. 44). The throne symbolizes heaven (no. 14). The four living creatures or cherubim symbolize the Word (no. 239). And the twenty-four elders symbolize the church in respect to all its constituents (no. 233, 251). It follows from this that the statement, "in the midst of the throne and of the four living creatures, and in the midst of the elders," means, symbolically, from the inmost elements in all the constituents of heaven, the Word, and the church.