What question has been asked a greater number of times, what idea has led men more to search the universe for an answer, what question is nearer and dearer to the human heart, what question is more inseparably connected with our existence, than this one, the immortality of the human soul?
It has been the theme of poets and sages, of priests and prophets; kings on the throne have discussed it, beggars on the street have dreamt of it. The best of humanity have approached it, and the worst of men have not hoped for it. The interest in the theme has not died, yet, nor will it die so long as human nature exists. Various answers have been presented to the world by various minds. Thousands, again, in every period of history have given up the discussion, and yet the question remains fresh as ever.
Often in the turmoil and struggle of our lives we seem to forget it, but suddenly someone dies--one, perhaps, whom we loved, one near and dear to our hearts, is snatched away from us--and the struggle, the din and turmoil of the world around us, cease for a moment, and the soul asks the old question, "What after this?" "What becomes of the soul?"
All human knowledge proceeds out of experience; we cannot know anything except by experience. All our reasoning is based upon generalised experience, all our knowledge is but harmonised experience. Looking around us, what do we find? A continuous change. The plant comes out of the seed, grows into the tree, completes the circles, and comes back to the seed. The animal comes, lives a certain time, dies, and completes the circle. So does man.
The mountains slowly but surely crumble away, the rivers slowly but surely dry up, rains come out of the sea, and go back to the sea. Everywhere circles are being completed, birth, growth, development, and decay following each other with mathematical precision. This is our everyday experience.
Inside of it all, behind all this vast mass of what we call life, of millions of forms and shapes, millions upon millions of varieties, beginning from the lowest atom to the highest spiritualised man, we find existing a certain unity. Every day we find that the wall that was thought to be dividing one thing and another is being broken down, and all matter is coming to be recognised by modern science as one substance, manifesting in different ways and in various forms; the one life that runs through all like a continuous chain, of which all these various forms represent the links, link after link, extending almost infinitely, but of the same one chain. This is what is called evolution. (Excerpt from a speech of Swami Vivekananda delivered in America)