Human life can be likened to a flowing river. What is a river?
A river, in fact, is a unique phenomenon of nature created by God. 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, nay, life-giving properties.
The same method is adopted by nature with regards to man. We know, human beings continue to be born generation after generation.
Life span for human beings is approximately a hundred years. Within period of a hundred years the previous generation is replaced with new men and Women. If the old water in a river is replaced with fresh water, in human beings this same occurrence takes place in the form previous generations yielding place to new generations.
A great wisdom lies behind this system set up in human life by God; its aim is that the coming generation should learn its lesson from the experiences of the previous generation.
Says Bhagavad Gita in chapter 13-18: A person who is not disturbed by the incessant flow of desires -- that enter like rivers into the ocean, which is ever being filled but is always still-- can alone achieve peace, and not the man who strives to satisfy such desires.
For instance, a father, in the light of his past experience, is able to give valuable advice to his overconfident son, saying that while confidence is good, overconfidence can result in failure.
The Holy Quran says God makes analogies using water. He likens the life on this world to the lifecycle of a plant: rain falls on a barren earth, bringing
to life a seed buried. The wise elderly are a valuable gift of nature to the energetic young.
If human life is like flowing water, it will remain fresh, but if it is stagnant in a closed space, it will become stale and unhealthy. Bible says whoever believes in me, as the scripture has said, out of his heart will flow rivers of living water. This is a beautiful lesson of nature for us, and the experience of human history testifies to this in practice.