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)

8421. 'And it shall be on the sixth day' means at the end of each state. This is clear from the meaning of 'day' is state, dealt with in 23, 487, 488, 493, 2788, 3462, 3785, 4850, 7680; and from the meaning of 'the sixth' as the end of a state. The reason why 'the sixth day' means the end of a state is that 'seven days' or 'a week' means a whole period or complete state, 2044, 3845, 6508, and therefore the day before the seventh, which is 'the sixth', means the end of that state, while the day after, which is 'the eighth', means the beginning of the same state, 2044, 8400.