The Isha Upanishad deems it necessary to utter a note of warn­ing in its third verse, which reads:

असुर्या नाम ते लोका अन्धेन तमसाऽऽवृता: । 3

‘Into the worlds of the asuras, enveloped in blinding darkness, veri­ly do they repair after death who are slayers of the Atman.’

In this verse we are warned as to what happens to us if we forget and neglect the Atman, if we ignore It, and live merely trivial lives. A deep philosophical truth is couched in mythical, symbolic language. Life lived without the consciousness of our divine nature is trivial; it is a life of darkness and sorrow. The word ‘darkness’ used in this verse is not physical darkness, but the darkness of ignorance; it is spiritual blindness.

Clutching at the shadows of sensate experience, taking them to be the whole of reality, man ignores the infinite, immortal dimension of his own personality. This is the meaning of samsara, worldliness, where man gets submerged in the objects of his ex­perience, and the subject, his real Self, is enveloped in the dark­ness of unawareness; this is spiritual suicide. As we have already seen, to live in the world is not the same thing as being ‘worldly’. To live in samsara is not the same thing as being a samsarin. As Sri Ramakrishna so beautifully expresses it in his parable, we all live in samsara, which means the world. The saint and the sinner, even an incarnation of God, lives in samsara. There is no harm in that, assures Sri Ramakrishna, but, he adds, samsara, the world, worldliness, should not live in us. A boat should be on water, but water should not be in the boat; for that is dangerous for the boat.

Worldliness is the negation of spiritual awareness. The ani­mal bodies are meant for mere sense-experience; they have no ex­perience of the subject. The world of objects comprises their sphere of awareness and of pleasure and pain. It is only in the human body that subjective awareness emerges, the awareness of self as different from the non-self. But in the early stages, this self is the little self, the ego which is mostly conditioned and constituted by the external world, the non-self. Man at this stage still functions at the animal level; he has, however, the requisite equipment and means to deepen his self-awareness and realise him­self as the Atman, the eternal, pure, luminous, ever-free Self, by controlling and disciplining his psycho-physical personality. But if, in spite of this capacity and opportunity, he fails to do so, and is content to submerge himself in the world of objects and things, he makes an utter fool of himself in spite of all his worldly success. This is spiritual suicide.

Reference: The Message of the Upanishads by Swami Ranganathananda (p.92,93,94)