Vivekananda was born in 1863 andbecame a great spiritual genius of his time. After his guru Sri Ramakrishna died he renounced everything and became a wandering monk, harboring a strong compassion for the people of India. He travelled to the West thereafter, taking the  opportunity to represent Hinduism at Chicago's Parliament of Religions in 1893.  He exhibited great spiritual and intellectual power in the west while spreading the Vedanta philosophy, and his powerful presence was widely recognized. He died in 1902 after showing the world the spiritual greatness for all to strive toward.
The soul of man is like a piece of crystal, but it takes the color of whatever is near it.  Whatever the soul touches... it has to take its color.  That is the difficulty.  That constitutes bondage.  The color is so strong, the crystal forgets itself and identifies itself with the color.  Suppose a red flower is near the crystal: the crystal takes the color and forgets itself, thinks it is red.  We have taken the color of the body and have forgotten what we are.  All the difficulties that follow come from that one dead body.  All our fears, all worries, anxieties, troubles, mistakes, weakness, evil, are from that one great blunder-- that we are bodies.  This is the ordinary person.  It is the person taking the color of the flower near to it.  We are no more bodies than the crystal is the red flower.
The Wisdom of Vivekananda
When a number of people from various angles and distances have a look at the sea, each man sees a portion of it according to his horizon.  Though each man may say that what he sees is the real sea, all of them speak the truth, for all of them see portions of the same wide expanse.  So the religious scriptures, though they seem to contain varying and conflicting statements, speak the truth, for they are all descriptions of that one infinite Reality.
The above passages are from the book Living At The Source Yoga Teachings of Vivekananda Edited by Ann Myren and Dorothy Madison Shambhala
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Every religion preaches that the essence of all morality is to do good to others.  And why? Be unselfish. And why should I? Some God has said it? He is not for me.  Some texts have declared it? Let them; that is nothing to me; let them all tell it.  And if they do, what is it to me? Each one for himself, and somebody take the hinder-most-- that is all the morality in the world at least with many. What is the reason that I should be moral? You cannot explain it except when you come to know the truth given in the Gita: "He who sees everyone in himself, and himself in everyone, thus seeing the same God living in all, he, the sage, no more kills the Self by the self." Know through Advaita that whosoever you hurt, you hurt yourself; they are all you. Whether you know it or not, through all hands you work, through all feet you move, you are the king enjoying in the palace, you are the beggar leading that miserable existence in the street; you are in the ignorant as well as in the learned, you are in the man who is weak, and you are in the strong; know this and be sympathetic. And that is why we must not hurt others. That is why I do not even care whether I have to starve, because there will be millions of mouths eating at the same time, and they are all mine. Therefore I should not care what becomes of me and mine, for the whole universe is mine, I am enjoying all the bliss at the same time; and who can kill me or the universe? Herein is morality.
Truth does not pay homage to any society,
ancient or modern.  Society has to pay
homage to Truth or die.  Societies should be
molded upon truth, and truth has not to adjust
itself to society.