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.

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

8610. 'And put it under him, and he sat on it' means correspondence with the highest level of truth. This becomes clear from the consideration that the stone supported Moses and 'Moses' represents the highest level of truth, which is God's truth that goes forth directly from the Lord. When the lowest level of truth corresponds with this highest level of truth it supports it, for they act as one. Interior truths are joined to exterior, and finally to the lowest through the correspondence [of each level with the one above it]. Highest truth then has might within the lowest, because it resides in it and acts through it. But if there is no such correspondence they are disjoined, and consequently highest truth has no might within lowest. What correspondence is may be seen from the extensive presentation, at the ends of a number of chapters, of the correspondence of all aspects of the human being with the Grand Man.