Enneads IV.8: Of the Descent of the Soul Into the Body
Sense-objects Are Necessary as Revealers of the Eternal
The excellence, power and goodness of intelligible (essences) are therefore revealed by sense-objects; and there is an eternal connection between intelligible (entities) that are self-existent, and sense-objects, which eternally derive their existence therefrom by participation, and which imitate intelligible nature to the extent of their ability.