That is an illustration drawn from the senses. As the whole body is in darkness, where the eye is not single, so if the soul has lost her original brightness, every sense, or that whole part of the soul to which sensation belongs, will abide in darkness.
Wherefore He says, “If then the light which is in thee be darkness, how great is that darkness!” that is, if the senses which are the soul’s light be darkened by vice, in how great darkness do you suppose the darkness itself will be wrapped?
Reproduced in full. Translation: Oxford 1841 (Newman), public domain (Public domain).