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)

60. Verse 31 And God saw everything that He had made, and behold, it was very good. And there was evening, and there was morning, a sixth day.

This verse says 'very good', whereas previous verses merely said 'good', for now the things of faith make one with those of love. A marriage has accordingly taken place between spiritual and celestial things.