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.

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

In Genesis 9:27, 'God spreading out Japheth' signifies his enlightenment. In a literal sense 'to spread out' signifies extending the borders, but in a spiritual sense, it signifies being enlightened. Enlightenment is the extension of the borders of wisdom and intelligence. In Isaiah 54:2, it signifies spiritual illumination or enlightenment. A member of the external church stretches out when he is instructed in the truths and goods of faith. As he is in charity, so he is more and more confirmed, and the more he is instructed, the more the cloud of his intellect is dissipated, which is where his charity and conscience resides.

(Reference: Arcana Coelestia 1101)