Hakeemul Ummah Hazrat Moulana Ashraf Ali Thaanwi Sahib رحمه الله has explained that there is effulgence (Noor) in the heart of a Musalli (one who performs Salaah). The effect of this Noor becomes discernable on the face as well. On the contrary, there is zulmat (darkness) in the heart of one who does not perform Salaah. The effect of this zulmat becomes manifest on the face as well.
The darkness of the face is indicative of there being fire inside the heart and the darkness of the face is its smoke. Such a person has darkened his body and soul. The effect of this darkness of the heart/soul is that such an individual has no detestation for bribery, lies or slander. He is unconcerned if he usurps someone’s property; nor has he any intention of fulfilling his debts. He stares with lust at young lads and women. Adopting the appearance of the kuffaar does not have any effect on him.
This is the paralysis of heedlessness and indifference in that the flames of sin are not perceived. The body becomes desensitised. But one day, this indifference and heedlessness will certainly disappear when the effects of the scorching flames of sin will be fully perceived at the time of death. It is thus imperative to persevere on nurturing modesty (Hayaa) in our lives; steadfastness on good deeds will be a source of illumination in every way.