From the tafsir of Qur'aan Made Easy and Ma'aariful Qur'aan:
On the Day of Judgement, there will be two separate groups of people, believers and unbelievers, and their faces will be different. This verse describes the faces of the unbelievers. They will be downcast. The word khEshi'ah from the root word khusha' mean 'to humble, humiliate, cast down'. This is the meaning of casting oneself down before Allah in prayer. People who did not cast themselves down before Allah in this world, their faces on the Day of Judgement will bedowncast with humiliation and disgrace.
The other conditions of the unbelievers are 'Amilah and Nasibah. The
word 'Amilah from 'Amal means 'to work hard' and 'Amil or 'Amilah in
Arabic is used for 'a person who works continuously, so as to become
completely tired'. The word Nasibah is derived from nasab. This word also
refers to 'one who toils unceasingly so as to become totally exhausted'. It
seems that the latter two conditions of the unbelievers relate to this world,
because Hereafter is not a realm in which one has to work to become so
tired and exhausted. Therefore, Qurtubi and other commentators are of
the view that the humbleness of their faces relates to the Hereafter, but
their working hard and being exhausted refers to their work in this world.
Given this interpretation, the sense is that many unbelievers exert themselves in their false rituals, and work hard in their presumed acts of worship in the world, as for instance the Hindu Yogis and many Christian monks do. They endure many difficulties in the devotional acts of worship sincerely in order to seek the good pleasure of Allah, but being on wrong
and idolatrous ways, they are not acceptable to, or rewarded by, Allah.
Thus their faces show signs of exhaustion in this world; and in the
Hereafter they will show signs of disgrace and humiliation.
Sayyiduna Hasan Basri reports that when Sayyiduna 'Umar
went to Syria, a Christian monk came to him. He was an old man, and
on account of his religious exercises and great endeavors, his face was
exhausted, his body was dry and his dressing was miserable. When
Sayyiduna 'Umar & looked at him, he began to weep. People asked him
about the cause of his weeping. He replied: "I pity the condition of this old
man. This poor soul worked so hard and showed such readiness to lay
down his life to achieve a particular purpose (that is, to gain the pleasure
of Allah) but, alas! He could not achieve it. Then he recited the following
Many faces on that day will be looking down (disgraced because of embarrassment and fear).
(Among these shall be) He who suffered affliction and who endured many difficulties (thinking that he was pleasing Allaah whereas his beliefs and actions did not conform with the injunctions of Allaah).