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)

2251. Verse 24 Perhaps there may be fifty righteous persons in the midst of the city. Will You also destroy and not spare the place for the sake of the fifty righteous persons who are in the midst of it?

'Perhaps there may be fifty righteous persons in the midst of the city' means that the truths may be full of goods. 'Will You also destroy and not spare the place for the sake of the fifty righteous persons who are in the midst of it?' means intercession made from love that in that case, they should not perish.