That which we believe is distinct from that which we understand. We can, for instance, believe in a material universe, but we can never understand it because the true universe is not material but spiritual.
A first step in Christian Science is to draw a clear distinction between the realm of understanding and the theories of mortal, material belief; to accept the one and to turn away from the other. Mary Baker Eddy writes in the Christian Science textbook, "Science and Health with Key to the Scriptures" (p. 28), "In conscience, we cannot hold to beliefs outgrown; and by understanding more of the divine Principle of the deathless Christ, we are enabled to heal the sick and to triumph over sin."
In some degree at least every mortal is aware of the difference between right and wrong, good and evil. He possesses an inward conviction, called conscience, which informs him of this fact. From whence comes this inward conviction named conscience? Is it in the realm of belief or understanding? Clearly it must originate in God, for it informs us of what is good.