The wise who knows the Self as bodiless within the bodies, as unchanging among changing things, as great and omnipresent, does never grieve. That self cannot be gained by the Veda, nor by understanding, nor by much learning. He whom the Self chooses, by him the Self can be gained. The Self chooses him (his body) as his own". But he who has not first turned away from his wickedness, who is not tranquil, and subdued, or whose mind is not at rest, he can never obtain the Self (even) by knowledge.
Katha Upanishad 1.2.22-24