For western people it may be more clear if i say that advaita is Panentheism (dvaita) first and then advaita, in contrast to Pantheism of visistaadvaita. Many people mistake advaita as Pantheism.
First the distinct difference between the immutable Being and its Mind (nature) must be grasped by discriminative process of Neti-Neti or Who Am I. Once the immutable is known there is no more any other second, as per experience of sages and as per sruti. The divisions that exist in mind does nothing to divide the reality. Reality remains untouched and as one. To know the reality is to first discard the conceptualisations of mind that superimpose on the reality to give an appearance of spanda and division.
Svetasvatara 4.18
When there is no darkness of ignorance, there is no day or night, neither being nor nonbeing; the pure Brahman alone exists. That immutable Reality is the meaning of "That"; It is adored by the Sun. From It has proceeded the ancient wisdom.
When there is no darkness, then there is no day or night, no being or non-being, only the kind one alone.That is the imperishable, the splendor of Savitri; from that came primal wisdom.
