P25: The greatest striving of the Mind, and its greatest virtue is understanding things by the third kind of knowledge.

Dem.: The third kind of knowledge proceeds from an adequate idea of certain attributes of God/Nature to an adequate knowledge of the essence of things (see its Def. in IIP40 S2), and the more we understand things in this way, the more we understand God/Nature (by P24).

Therefore (by IVP28), the greatest virtue of the Mind, i.e. (by IVD8), the Mind’s power, or nature, or (by IIIP7) its greatest striving, is to understand things by the third kind of knowledge, q.e.d.