"Thus the sum of things is ever being reviewed, and mortals dependent one upon another. Some nations increase, others diminish, and in a short space the generations of living creatures are changed and like runners pass on the torch of life"

This quote is suggesting that everything out there is continuously changing and progressing, with some things growing while others decrease. It emphasizes the interconnectedness of all things, with each being dependent on the others. The referral to "passing on the torch of life" recommends that the cycles of life and death are ongoing, with each generation acquiring and passing on the tradition of those that came before.