Human life can be likened to a flowing river. What is a river? A river is a unique phenomenon of nature. In the river fresh water is being added to the existing water at every moment.
This everyday phenomenon is responsible for the freshness of the river water. In the absence of this continuous flow of newly added water, the river will lose its freshness: it will not be able to maintain its health-giving, even life-giving, properties.
The same method is adopted by nature with regard to human beings. As we know, human beings continue to be born, generation after generation. Within a period of a hundred years, the previous generation is replaced by a fresh set of people. If the old water is replaced with fresh water, in human beings this same occurrence takes place in the form of previous generations yielding place to new generations.