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)

10641. 'Lest by chance it become a snare in your midst' means consequently being led astray in the Word itself. This is clear from the meaning of 'becoming a snare' as being held captive and led astray by one's own evil and falsity, dealt with in 7653, 9348; and from the representation of 'Moses' as the Word, dealt with in the places referred to in 9372, so that 'in his midst' means in the Word itself. The implications of this are clear from what has been stated immediately above in 10640.