P15: He who understands himself and his affects clearly and distinctly loves God/Nature, and does so the more, the more he understands himself and his affects.

Dem.: He who understands himself and his affects clearly and distinctly rejoices (by IIIP53), and this Joy is accompanied by the idea of God/Nature (by P14). Hence (by Def. Aff. VI), he loves God/Nature, and (by the same reasoning) does so the more, the more he understands himself and his affects, q.e.d.