The core argument rests on the Law of Continuity, which asserts that the fundamental laws of the natural universe do not abruptly terminate at the boundaries of the spiritual world. Instead, spiritual laws are the natural laws extended into a higher sphere. Drummond uses this premise to examine various spiritual phenomena through the lens of modern biology and physics.
The central thesis focuses on biogenesis, demonstrating that just as physical life can only arise from pre-existing physical life, spiritual life requires contact with a living source. A dead soul cannot spontaneously generate life from within itself, making regeneration a biological necessity rather than a mere philosophical metaphor.
Building upon this framework, the text addresses the concept of degeneration. When an organism neglects its environment, it inevitably suffers a regression to a simpler or degraded type. In the spiritual domain, moral and religious neglect leads to the atrophy of spiritual faculties and eventual spiritual death.
Growth is another central theme examined via natural parallels. True spiritual growth occurs spontaneously and mysteriously, similar to the development of a plant. Efforts driven purely by human anxiety and mechanical struggle fail to add anything to the spiritual stature, which instead relies on maintaining the correct position relative to the environment.
Mortification and the limitation of correspondences are presented as necessary mechanisms for breaking ties with an inimical environment. Since physical death is not immediate upon conversion, the believer must actively suppress destructive habits and selfish desires by starving them of nutritive interactions.
Finally, the work defines eternal life not merely as endless duration, but as perfect and uninterrupted correspondence with a perfect environment. Knowing God constitutes this ultimate life, bridging the temporal and the eternal through a permanent alignment with the divine source.
