Kabbalah do Liczb 15:39

Another correction for the sign of the Brit is to be of lowered eyes, because by the sight of the eye one comes to damage the Brit, as it says “and do not follow after your eyes and after your heart” (Numbers 15:39), since the eye and heart are the two main causes of sin. When the eye damages he is called “Ra Ayin” (evil eye), as it says “do not eat bread from one who has evil eye” (Proverbs 23:6), and the reason is that just like the damage of the Brit is called Ra (evil) so too the damage of the pupil of the eye, which is Yud, is called Ra (evil), since he uses his holy vision in vain and to a place of nakedness, etc. Since we find that the correction of the Brit is “depart from evil”, it includes that he should not have an evil eye, and that is “depart from evil”—any type of evil, whether the eye or the tongue, as it says “guard your tongue from evil”, and including the Brit since all these can become evil, as we explained.