The witness of the three states of consciousness [waking, dream and deep sleep] and of the nature of Existence-Consciousness-Bliss is the Self
All the manifested world of things and beings are projected by imagination upon the substratum which is the Eternal All-pervading Vishnu, whose nature is Existence-Intelligence; just as the different ornaments are all made out of the same gold.
As gold purified in a furnace loses its impurities and achieves its own true nature, the mind gets rid of the impurities of the attributes of delusion, attachment and purity through meditation and attains Reality.
There is sorrow in finitude. The Self is beyond time, space and objects. It is infinite and hence of the nature of absolute happiness.
Each thing tends to move towards its own nature. I always desire happiness which is my true nature. My nature is never a burden to me. Happiness is never a burden to me, whilst sorrow is.
Thus one should know oneself to be of the nature of Existence-Consciousness-Bliss [Sat-Chit-Ananda].