What harms the senses is bad for creatures that feel. What blocks desire and action is bad for creatures that feel. Just as with feeling creatures, whatever harms plants is bad for plant nature. In the same way, whatever blocks the mind is the real enemy of rational beings.
That which is a hindrance of the senses, is an evil to the sensitive nature. That which is a hindrance of the appetitive and prosecutive faculty, is an evil to the sensitive nature. As of the sensitive, so of the vegetative constitution, whatsoever is a hindrance unto it, is also in that respect an evil unto the same. And so likewise, whatsoever is a hindrance unto the mind and understanding, must needs be the proper evil of the reasonable nature.