इदमहं पदाभिख्यमन्वहम् ।अहमिलीनकेऽप्यलयसत्तया ॥
इदम् अहम् पदाभिख्यम् अन्वहम् अहमि लीनके अपि अलयसत्तया
In plain words
Every night the one that says 'I' goes under completely. That is not a theory; it happens to everyone. And something did not go under, or there would be nobody to have slept. So the word 'I' has never been pointing at the thing that disappears. It has been pointing at what stayed.
Word for word
This is what the word 'I' denotes, always — even when the 'I' has merged, by its unmerged existence.