Thought process is exclusive to human beings. One can use it for betterment of himself or for the benefit of the society and future generations or for self destruction and destruction of the society. Everything and every action starts from a thought. Ancient sages of India have spent thousands of years(they used to live for twenty thousand years on an average which may come as a surprise for modern generation) in meditation and uncovered so many facts about self or the soul, nature and atoms(atomic theory of Kanada who said the universe is made of biatomic and triatomic molecules, which in the modern ages became atomic bomb). Like this there are several examples of sages looking inwards during the meditation and uncovered the truths like for example what happens during deep sleep and an additional state of mind called interval state between the awakened and deep sleep state(antharala avastha) as opposed to normal thinking of the three states of mind(awakened, dream and deep sleep). Western philosophers in the last few hundred years were totally unaware of subtle facts of philosophy/spirituality like this.

Another aspect of the thought as said earlier is destructive aspect. World wars have started because of the thought which Hitler had. Or even the wars that are going on the in the most recent years are because diversion of the thought process by the narrow minded selfish individuals or religious fanatics, towards the wars mode. Mahatma Gandhi achieved independence for India purely by his thoughts of non violence. Maharshis like Ramana sat in one place and concentrated for the welfare of the society and with total silence and by his sheer looks, he converted a journalist called Balakrishna Menon into a prominent saint like Chinmayananda swami who did the world so much good and protected the Arshadharma for the future and Ramakrishna Paramahamsa made Yathi Vivekananda who enlightened the western world and made them appreciate the Sanathana Dharma and became world famous person. Like this there are plenty of examples.

Coming to the connection of thought and spirituality particularly for the one who wants to achieve the final stage of Advaitha which is to remain in the state of swaroopa(being in the state of primordial self), the thought(mind) is the key. Because it is absolute silence without any movement of the mind, It is not acceptable to the mind as it is addicted to wander and run from one to the other, be it the name, form, or memories of good and bad or thinking about the future. The mind wants to destabilize the silence. It wants to see within itself the semigods and demigods who will sanction all its wishes or chant a mantra or plan for a pilgrimage or go for a cinema. It cannot accept the absolute silence of Atman.

The absolute silence is described as the one where in the state of mind is such "Yatra mata amata bhavanthi, yatra pita apita bhavanthi, yatra veda aveda bhavanthi, yatra deva adeva bhavanthi". It means the mother is no longer the mother, the father is no longer the father, Vedas are no longer Vedas, and gods are no longer gods. That means there is no perception of all these any longer. That is the blissful state of Samadhi where there is nothing else except pure awareness. It is where there is no idea of names, forms, sounds, taste etc. If one can achieve this, then the mind automatically disappears. To keep it in that state all the time is Samadhi. There is one fundamental difference one should be aware of is the difference between the deep sleep and Samadhi. In sleep it is tamasic guna that is predominant in the individual(inertia, ignorance, dull, inactive etc). In Samadhi it is sattva guna that is predominant(Sattva guna is charecterised by virtue, intelligence, goodness, and creates a balance of harmony, and stability). One has to practice to become sattvic by being unselfish, being aware of himself or acquiring self knowledge from Upanishads and from teachers who know the method of teaching them and teach them. Sleep is dark and Samdhi is illuminated by eternal consciousness or Satchitananda.

To remain in Samadhi at all times is the final accolade of advaitha and that is being God or achieving Moksha or being liberated and experiencing “Aham Brahmasmi” So this is what a thought(mind where it originates) can do. It can either make a man a saint or a sinner. One has to make one’s own choice what to become and how to use or divert his thoughts.