Full Idea
For Descartes the essence of corporeal things is not an object of the senses, but only of the mind; and hence it is not the senses but the mind that is the essence of the perceiving subject, that is, of man.
Clarification
'Corporeal things' are physical objects
Gist of Idea
For Descartes a person's essence is the mind because objects are perceived by mind, not senses
Source
report of René Descartes (Meditations [1641], 2) by Ludwig Feuerbach - Principles of Philosophy of the Future §17
Book Reference
Feuerbach,Ludwig: 'Principles of the Philosophy of the Future', ed/tr. Vogel,M [Hackett 1986], p.26
A Reaction
This, of course, is why Descartes' approach can lead to idealism and solipsism, whereas the other approach leads to empiricism and animalism (Idea 6669).
Related Idea
Idea 6669 For 'animalism', I exist before I became a person, and can continue after it, so I am not a person [Olson, by Lowe]