In plain words
Students!
The coming together of body, mind and Ātma is humanness. These are what shape man's nature. Not only shaping it, but settling man's nature and lifting him to a higher level: that too is the work of these three alone. What performs actions is the body. What knows is the mind. What is, is the Ātma. This Ātma itself is the divinity in man. Humanness is the manifestation of the three powers: doing, knowing and being. It is this that moulds man into a full human being. In the language of the spirit this has been called Kriyā-śakti, Icchā-śakti and Jñāna-śakti. Without Icchā-śakti, Kriyā-śakti does not come about. Without Jñāna-śakti, Icchā-śakti takes no form. In short, Kriyā-śakti, Icchā-śakti and Jñāna-śakti rest one upon another, support each other mutually, and so they grow. They are inseparably bound; they support each other. If any one of the three, Kriyā-śakti, Icchā-śakti, Jñāna-śakti, is wanting, man cannot reach its fullness.
In the world we use many words. In grammar, every sentence has three things joined in it: subject, object and verb. A small example. Rāmulu beat the dog. It is only by the unity of these three that the sentence becomes complete. If instead you say "Rāmulu beat", the question arises, "Whom?" If instead you say "Rāmulu the dog", the question arises, "What did he do?" If you say only "Rāmulu", the question arises, "What did he do?" The words stand without any link between them. If you say "beat the dog", the question arises, "Who?" Whichever word is missing here, the sentence is not complete. So subject, object and verb, these three, must be there. So, in every man, without this Kriyā-śakti, Icchā-śakti and Jñāna-śakti humanness can never be complete. Icchā-śakti is like a body of diamond. Through Icchā-śakti alone, Jñāna-śakti, Kriyā-śakti, the power of intellect, the power of speech, the power of resolve, all powers arise from Icchā-śakti itself. And this mind is made of resolves hard as diamond. Even when a man dies, his resolve does not die. It takes on an everlasting form. In the spiritual life such a mind has been given the very highest place.
But the scientists have been comparing the mind in another way. They speak of it as a chemical and biological composition.