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)

9834. 'And they shall make the ephod from gold, violet, and purple, twice-dyed scarlet, and fine twined linen' means the outermost part of the spiritual kingdom springing from that good. This is clear from the meaning of 'the ephod' as the outermost part of the spiritual kingdom, dealt with in 9824; from the meaning of 'gold' as good, at this point the good reigning universally, dealt with above in 9832; and from the meaning of 'violet, purple, double-dyed scarlet, and fine twined linen' as the good of charity and faith, dealt with immediately above in 9833. This is why it is said to spring from 'that' good.