A stable natural environment serves as the "engine" for human continuity, technology, and science. We must "care for it as an egg" because it serves as a powerful platform for our development.
An egg is a self-contained life-support system that must be kept at the right temperature and handled gently to hatch. Similarly, Earth is a closed system that requires precise balance to sustain the technological and scientific progress we crave.
We must protect the "shell" (the atmosphere and biosphere) to ensure what is inside (human potential) can thrive.
Nature is a resource, it is actually the vessel of our future. It is the vital link between our environmental stability, human continuity, and the pursuit of science and technology.