A Concise but comprehensive definition of substance is given by Mary Baker Eddy on page 468 of "Science and Health with Key to the Scriptures," as follows: "Substance is that which is eternal and incapable of discord and decay." Since no form of matter is eternal, and since all forms of matter are subject to discord and decay, it is obvious that matter is not substance. Nothing inert or mindless has any relationship to real substance. Real substance cannot be weighed or measured. It is imponderable and infinite. It is boundless, limitless, unconfined, universal, invisible, indivisible, spiritual, undecaying, incorruptible, indestructible, eternal. Since everything in the so-called material world is finite, temporal, evanescent, nothing in this world is actually or really substantial.
Nothing that relates to a finite, material, temporal sense of existence is truly substantial. Nothing that can be discerned by the material senses, nothing that has beginning and end, nothing that is subject to fluctuation, variability, diminution, is in any way related to real substance. Substance is that which is basic or foundational; that which "stands under" or underlies all. That which is basic and foundational to reality is Mind, Spirit, God. Therefore Mind, not matter, is substance.
Since Mind, divine Principle, is the only basis or foundation of reality, that only which proceeds from Principle is really substantial. That which proceeds from Principle, or Mind, is idea. Therefore, spiritual ideas alone are substantial, and one who reflects and in that sense embodies spiritual ideas, true thoughts, is indeed expressing or manifesting real substance. He has understanding. The Bible says, "Give me understanding, and I shall live;" and it also says, "Get wisdom: and with all thy getting get understanding."
