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)

A company might have executives setting policy and strategy, engineers designing products, managers handling personnel and others handling various functions. They all do different things -- but if they're doing them with a shared underlying purpose, the company -- and the individuals in it -- will likely be successful. The Lord wants all human society to function in a similar way. We have different skills and individual loves, but if we all share a mutual love -- a love of serving others -- then society will function as one, will be a reflection of heaven and will be a good receptacle for the Lord's love. This can also happen within each of us, as we unify our talents and ideas around a central love. And in an abstract sense, it illustrates how a wide collection of varying ideas can be unified around a shared good intention. That is the kind of love pictured when “one” is used in the Bible, either as a specific number or in the sense of several people or objects “being one.” In more casual references -- when used to identify a specific person or object -- the meaning is relatively literal, and is connected to that person or object.