As the same sun appears as different when shining on different media, such as water and oil, so the same omnipresent Being, shining through different nervous systems, appears as different and forms the spirit, the subjective aspect of man's personality. When the nervous system is pure, Being reflects more and the spirit is more powerful, the mind more effective. When the nervous system is at its purest, then the Being reflects in all its fullness, and the inner individuality of the spirit gains the level of unlimited eternal Being. Thus it is clear that in its essential nature the spirit is undying and omnipresent. This explains the universality of individuality.

~ Maharishi Mahesh Yogi
[Commentary on Bhagavad Gita, Ch2, V17]

When the intellect, bewildered by the multiplicity of holy scripts, stands unperturbed in blissful contemplation of the Infinite, then hast thou attained Spirituality.

~ Bhagavad Gita

[Trans. Purohit Swami Ch2, V2]