This objective knowledge of the self is what the author means when he says:
“No one can know himself unless he knows what, and not who, he is, on what he depends, or whose he is [or: to whom or what he belongs] and for what end he was made.”
The distinction between “quis” and “quid” is crucial: whereas “quis” has an unmistakably personal aspect and refers to the ego, “quid” is neuter, predicating nothing except an object which is not endowed even with personality.
Not the subjective ego-consciousness of the psyche is meant, but the psyche itself as the unknown, unprejudiced object that still has to be investigated.
The difference between knowledge of the ego and knowledge of the self could hardly be formulated more trenchantly than in this distinction between “quis” and “quid.”
An alchemist of the sixteenth century has here put his finger on something that certain psychologists (or those of them who allow themselves an opinion in psychological matters) still stumble over today.
“What” refers to the neutral self, the objective fact of totality, since the ego is on the one hand causally “dependent on” or “belongs to” it, and on the other hand is directed towards it as to a goal.
This recalls the impressive opening sentence of Ignatius Loyola’s “Foundation”: “Man was created to praise, do reverence to, and serve God our Lord, and thereby to save his soul.” ~Carl Jung, CW 9ii, Para 252