In the first chapter of Genesis we read, "And God said, Let there be a firmament in the midst of the waters, and let it divide the waters from the waters." "Firmament" Mary Baker Eddy defines in "Science and Health with Key to the Scriptures" (p. 586) as "spiritual understanding; the scientific line of demarcation between Truth and error, between Spirit and so-called matter." This does not mean that Truth is conscious of error or that Spirit recognizes matter, but rather that there is no commingling of Truth with error or Spirit with matter. There is a sharp line of separation between the two, and as Truth, Spirit, becomes All-in-all to us, there will be no consciousness of anything else.
Let us then think of spiritual understanding as this line of demarcation. Spiritual sense testifies to reality, and material sense to unreality. Spiritual sense has no record of unreality, and material sense, or the five senses, cannot cognize reality. And yet mortals, until their thinking is corrected by Christian Science, look to material sense for information from which they attempt to shape their lives. The gaining of spiritual understanding requires mortals to turn to spiritual sense. "Spiritual sense," says Mrs. Eddy (ibid., p. 209), "is a conscious, constant capacity to understand God."
When the reality of spiritual sense, rather than the unreality of material sense, is the directing influence in a life, harmony, peace, joy, achievement, and dominion characterize that life. Why? Because to appear real the claims of unreality must be accepted. If these claims are rejected as worthless and unreal, they cannot even seem to objectify themselves in our experience.
