And God said, “Let there be an expanse in the middle of the waters, and let it exist to make a distinction among the waters, in the waters.” — Genesis 1:6
The next step occurs after the Spirit of God—the Lord’s mercy—brings out into daylight the knowledge of truth and goodness and provides the first glimmering that the Lord exists, that he is goodness and truth itself, and that nothing is good or true except what comes from him. The Spirit of God then makes a distinction between the inner and the outer being, and between the religious knowledge we possess in our inner selves and the secular knowledge belonging to our outer selves.
The inner self is called the expanse, the knowledge in the inner self is called the waters over the expanse, and the facts belonging to the outer self are called the waters under the expanse.
Before we are reborn, we do not know even that an inner being exists, let alone what it is, imagining there is no difference between the two selves. This is because we are absorbed by bodily and worldly interests and merge the concerns of the inner being with those interests. Out of distinct and separate planes we make one dim, confused whole.
Therefore this verse first says that there should be an expanse in the middle of the waters, then that it should exist to make a distinction “among the waters, in the waters,” but not that it should make a distinction between one set of waters and another.
from Secrets of Heaven, Volume 1, Section 24