By which knowledge of the Self as non-existence and the non-Self as existence,
Then this is non-knowledge, just as a rope is erroneously seen as a snake.
Commentary
Shankaracharya declares in the Vivekachudamani (verse 138) that "it is absence of intuitive judgement which makes one mistake a rope for a snake." The Niralamba Upanishad declares, "non-knowledge is a dualistic misapprehension due to various conditionings, like the snake and rope (error) or the (concept) of many Selfs." Non-knowledge leaves one in ignorance, knowledge takes one out of ignorance, and when the two are transcended, the Absolute is attained.