P28: Knowledge of God/Nature is the Mind’s greatest good; its greatest virtue is to know God/Nature.

Dem.: The greatest thing the Mind can understand is God/Nature, i.e. (by ID6), a Being absolutely infinite, without which (by IP15) it can neither be nor be conceived. And so (by P26 and P27), the Mind’s greatest advantage, or (by D1) good, is knowledge of God/Nature.

Next, only insofar as the Mind understands (by IIIP1 and P3), does it act, and can it be said absolutely to act from virtue (by P23). The absolute virtue of the Mind, then, is understanding. But the greatest thing the Mind can understand is God/Nature (as we have already demonstrated). Therefore, the greatest virtue of the Mind is to understand, or know, God/Nature, q.e.d.