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)

3197. 'Towards evening' means as compared with the things below it. This is clear from the meaning of 'evening' as obscurity, dealt with in 3056. And since the things of a lower nature in a person, namely those belonging to his natural mind, are in obscurity as compared with the things of a higher nature, namely those belonging to his rational mind, 'evening' therefore means those things which, compared with them in other states, are in obscurity, as may be seen from the train of thought in the internal sense. For the subject in the internal sense is truth from the natural that was to be joined to good in the rational. And since the subject at this point is the joining together of these two, and the enlightenment of the natural man through the rational, 'meditating in the field towards evening' therefore means a state of the rational that is immersed in good as compared with the things below it. The state of immersion in good is described by Isaac's dwelling 'in the land of the south', that is, dwelling in Divine light. Compared with this the things below the Rational dwelt in evening shade, before, that is, truth and good had been joined together and before the Natural too had been made Divine.