These are the two subjects of study for man, external and internal nature; and though at first these seem to be contradictory, yet external nature must, to the ordinary man, be entirely composed of internal nature, the world of thought. The majority of philosophies in every country, especially in the West, have started with the assumption that these two, matter and mind, are contradictory existences; but in the long run we shall find that they converge towards each other and in the end unite and form an infinite whole. So it is not that by this analysis I mean a higher or lower standpoint with regard to the subject. I do not mean that those who want to search after truth through external nature are wrong, nor that those who want to search after truth through internal nature are higher. These are the two modes of procedure. Both of them must live; both of them must be studied; and in the end we shall find that they meet. We shall see that neither is the body antagonistic to the mind, nor the mind to the body, although we find, many persons who think that this body is nothing. In old times, every country was full of people who thought this body was only a disease, a sin, or something of that kind. Later on, however, we see how, as it was taught in the Vedas, this body melts into the mind, and the mind into the body. (VI, 4)
Unification always leads to peace and happiness. It is the divisive thought processes that create unhappiness and misery. Unification is our goal. Sri Ramakrishna used to say “Tie Advaita in one corner of your dress and then do all your work.” Swamiji also advises us to keep unity as the prime thought, unify our mind and body and then the whole Universe.