The whole universe is one. There is only one Self in the universe, only One Existence, and that One Existence, when it passes through the forms of time, space, and causation, is called by different names, buddhi, fine matter, gross matter, all mental and physical forms. Everything in the universe is that One, appearing in various forms. When a little part of it comes, as it were, into this network of time, space, and causation it takes forms; take off the network, and it is all one.
After every happiness comes misery; they may be far apart or near. The more advanced the soul, the more quickly does one follow the other. What we want in neither happiness or misery. Both make us forget our true nature; both are chains – one iron , one gold. Behind both is the Atman, who knows neither happiness nor misery. These are states and states must ever change; but the nature of the soul / Atman is bliss, peace, unchanging. We have not to get it, we have it, only wash away the dross and see it.
Therefore in the Advaita philosophy, the whole universe is all one in the Self which is called Brahman. That Self when it appears behind the universe is called God. The same Self when it appears behind this little universe, the body, is the soul. This very soul, therefore, is the Self in man. As a man sees his own face in a mirror, perfect, distinct, and clear, so is the Truth shining in the soul of man. The highest heaven, therefore, is in our own souls; the greatest temple of worship is the human soul