In the Bible, things that are lower down, or under, physically, generally represent things that are lower or more external spiritually. In some cases, the lower things have been separated and put away to protect the good, but in others, it can mean that a less exalted idea or good desire is supporting a more exalted one.

(Референце: Arcana Coelestia 4564 [1-2], 8610, 9656)

9655. 'And you shall make two boards for the corners of the dwelling-place at the two legs' means the essential nature of the joining to good there. This is clear from what comes next, where it says that the boards there 'shall be paired from below, and at the same time paired up to its head to one ring', which describes the essential nature of the joining to good there. For 'two' means a joining together, 9645, 'boards' good that lends support, 9634, and 'the corners of the dwelling-place at the two legs' the borders where that good exists, 9653.