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)

5344. 'Which was round about it he laid up in the midst of it' means that what existed first in the exterior natural was stored away by it in the interior parts of the interior natural. This is clear from the meaning of 'round about' as things on the outside and so in the exterior natural; and from the meaning of 'the midst' as things on the inside, dealt with in 1074, 2940, 2973, and so in the interior natural. The reason 'in the midst of it (the city)' means in the interior parts of the interior natural is that 'a city' means the interior parts, 5297, 5342. The interior parts of the interior natural are those parts in it which are called spiritual ones, and the spiritual parts in it are those parts which belong to the light of heaven and are therefore able to shed light on the parts there which belong to the light of the world, which strictly speaking are called natural ones. It is in the spiritual parts of the interior natural that the truths linked to good have been stored away.

[2] Those spiritual parts there are what correspond to the angelic communities in the second heaven, and a person is in communication with this heaven through his remnants. This heaven is the one that is opened when a person is being regenerated, and it is the one that is shut when a person does not allow himself to be regenerated. For remnants - that is, truths and forms of good stored away in interior parts - are nothing else than correspondences with the communities belonging to that heaven.