All essential knowledge relates to existence, or only such knowledge as has an essential relationship to existence is essential knowledge. Christendom has done away with Christianity without being quite aware of it.
Man is spirit.
Spirit is the self. Nowadays not even a suicide kills himself in desperation. Before taking the step he deliberates so long and so carefully that he literally chokes with thought. It is even questionable whether he ought to be called a suicide, since it is really thought which takes his life. He does not die with deliberation but from deliberation.