What then is the deeper distinction drawn by Christianity? What is the essential difference between the Christian and the not-a-Christian, between the spiritual beauty and the moral beauty? It is the distinction between the Organic and the Inorganic. Moral beauty is the product of the natural man, spiritual beauty of the spiritual man. And these two, according to the law of Biogenesis, are separated from one another by the deepest line known to Science. This Law is at once the foundation of Biology and of Spiritual religion. And the whole fabric of Christianity falls into confusion if we attempt to ignore it. The Law of Biogenesis, in fact, is to be regarded as the equivalent in biology of the First Law of motion in physics: _Every body continues in its state of rest or of uniform motion in a straight line, except in so far as it is compelled by force to change that state._ The first Law of biology is: That which is Mineral is Mineral; that which is Flesh is Flesh; that which is Spirit is Spirit. The mineral remains in the inorganic world until it is seized upon by a something called Life outside the inorganic world; the natural man remains the natural man, until a Spiritual Life from without the natural life seizes upon him, regenerates him, changes him into a spiritual man. The peril of the illustration from the law of motion will not be felt at least by those who appreciate the distinction between Physics and biology, between Energy and Life. The change of state here is not as in physics a mere change of direction, the affections directed to a new object, the will into a new channel. The change involves all this, but is something deeper. It is a change of nature, a regeneration, a passing from death into life. Hence relatively to this higher life the natural life is no longer Life, but Death, and the natural man from the standpoint of Christianity is dead. Whatever assent the mind may give to this proposition, however much it has been overlooked in the past, however it compares with casual observation, it is certain that the Founder of the Christian religion intended this to be the keystone of Christianity. In the proposition _That which is flesh is flesh, and that which is spirit is spirit_, Christ formulates the first law of biological religion, and lays the basis for a final classification. He divides men into two classes, the living and the not-living. And Paul afterward carries out the classification consistently, making his entire system depend on it, and throughout arranging men, on the one hand as πνευματικός--spiritual, on the other as ψυχικός--carnal, in terms of Christ's distinction.