These words are so lovely from Mundaka upanishad:
” Like two birds of golden plumage, inseparable companions, the individual self and the immortal Self are perched on the branches of the selfsame tree. The former tastes of the sweet and bitter fruits of the tree; the latter, tasting of neither, calmly observes.
The individual self, deluded by forgetfulness of his identity with the divine Self, bewildered by his ego, grieves and is sad. but when he recognises the worshipful Lord as his own true Self, and beholds his glory, he grieves no more.
When the seer beholds the Effulgent One, the Lord, the Supreme Being, then, transcending both good and evil, and freed from impurities, he unites himself with him.
The Lord is the one life shining forth from every creature. Seeing him present in all, the wise man is humble, puts not himself forward. His delight is in the Self, he serves the Lord in all. Such as he, indeed, are the true knowers of Brahman.
This Effulgent Self is to be realised within the lotus of the heart by continence, by steadfastness in truth, by meditation, and by superconscious vision. Their impurities washed away, the seers realise him.”
Note the use of the lower case ‘s’ in the individual self, and the capital ‘s’ in the immortal Self.