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)

10411. 'And built an altar in front of it' means worship. This is clear from the meaning of 'an altar' as the chief representative of Divine worship, dealt with in 4541, 8935, 8940, 9714, 10242, 10245, but at this point that which is representative of devilish worship since those whose interest lies in external things and not in what is internal are in contact with the hells and not with the heavens. (For a person's internal is his heaven, and his external is his world. His internal furthermore has been so created as to conform to an image of heaven, thus to receive such things as belong there, and his external to conform to an image of the world, thus to receive such things as belong here, see in the places referred to in 9279, 10156. Consequently when the internal is closed, so is heaven, and then the external is no longer ruled from heaven but from hell.) Therefore their worship is not Divine but devilish. They do, it is true, speak of the Divine and also offer Him worship, but outwardly and not inwardly, that is, with their lips but not with their heart. Nor do they worship ¹ the Divine for His sake but for the sake of themselves and the world. Where the heart is, in that place there is worship. From all this it is evident that 'building an altar in front of the golden calf' means worship of the devil.

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