Man, equipped with divine selection, is the only cultivator in Nature. Nature does all growing herself, and assigns all cultivating to Man.
But:
He cultivates only through removing deterrents to growth.
Man's value, as assistant in evolution, consists in his ability to create harmonic conditions favorable to growth through the exercise of divine selection.
But:
He secures perfect harmony only by first harmonizing himself.
Happiness is "the aim and the end of existence."