The power of the analogy, for which we are laying the foundations, to seize and impress the mind, will largely depend on the vividness with which one realizes the gulf which Nature places between the living and the dead.[36] But those who, in contemplating Nature, have found their attention arrested by this extraordinary dividing-line severing the visible universe eternally into two; those who in watching the progress of science have seen barrier after barrier disappear--barrier between plant and plant, between animal and animal, and even between animal and plant--but this gulf yawn more hopelessly wide with every advance of knowledge, will be prepared to attach a significance to the Law of Biogenesis and its analogies more profound perhaps than to any other fact or law in Nature. If, as Pascal says, Nature is an image of grace; if the things that are seen are in any sense the images of the unseen, there must lie in this great gulf fixed, this most unique and startling of all natural phenomena, a meaning of peculiar moment. Where now in the Spiritual spheres shall we meet a companion phenomena to this? What in the Unseen shall be likened to this deep dividing-line, or where in human experience is another barrier which never can be crossed? There is such a barrier. In the dim but not inadequate vision of the Spiritual World presented in the Word of God, the first thing that strikes the eye is a great gulf fixed. The passage from the Natural World to the Spiritual World is hermetically sealed on the natural side. The door from the inorganic to the organic is shut, no mineral can open it; so the door from the natural to the spiritual is shut, and no man can open it. This world of natural men is staked off from the Spiritual World by barriers which have never yet been crossed from within. No organic change, no modification of environment, no mental energy, no moral effort, no evolution of character, no progress of civilization can endow any single human soul with the attribute of Spiritual Life. The Spiritual World is guarded from the world next in order beneath it by a law of Biogenesis--_except a man be born again ... except a man be born of water and of the Spirit, he cannot enter the Kingdom of God_.