Surah 68. Al-Qalam, Ayah 42

I.e., willingly, gladly humbling themselves before Him.

Lit., "when the shin[-bone] shall be bared": i.e., when man's innermost thoughts, feelings and motivations will be laid bare. The implication is that their erstwhile claim that whatever is "expedient" is morally justifiable (see note [19] above), shall be revealed in all its nakedness - namely, as something indefensible and spiritually destructive.

 Like the Face and the Hands, the Shin is believed by many to be one of the qualities of Allah, in a way befitting His Majesty and Greatness. Since baring the shin in the Arab culture is associated with the heat of battle, some interpret the verse metaphorically, so the meaning would be: “˹Beware of˺ the Day when horror sets in.”

"The Day that the Shin shall be laid bair", that is, when men are confronted with the stark reality of the Day of Judgment. On that occasion men will be summoned to adoration, not necessarily in words, but by the logic of facts, when the Reality will be fully manifest: the Glory will be too dazzling for the Unbelievers, whose past deliberate refusal, when they had freedom to choose and yet rejected, will stand in way.