Or; The eye He speaks of is not the external but the internal eye. The light is the understanding, through which the soul sees God. He whose heart is turned to God, has an eye full of light; that is, his understanding is pure, not distorted by the influence of worldly lusts. The darkness in us is our bodily senses, which always desire the things that pertain to darkness.
Whoso then has a pure eye, that is, a spiritual understanding, preserves his body in light, that is, without sin; for though the flesh desires evil, yet by the might of divine fear the soul resists it. But whoever has an eye, that is, an understanding, either darkened by the influence of the malignant passions, or fouled by evil lusts, possesses his body in darkness; he does not resist the flesh when it lusts after evil things, because he has no hope in Heaven, which hope alone gives us the strength to resist desire.
Reproduced in full. Translation: Oxford 1841 (Newman), public domain (Public domain).