In يَوْمَئِذٍ يَوَدُّ الَّذِينَ كَفَرُوا ، the text mentions the state of utter despair faced by disbelievers on the Last Day. That day they would wish to go extinct rather than face its ordeal, to become a patch of the earth underneath, or wish that the earth would crack open, suck them in leaving nothing on top but dust mingled with dust, so that they would be delivered of the scrutiny and retribution of that fateful time. (The statement: لَوْ تُسَوَّىٰ بِهِمُ الْأَرْضُ (42) has been translated here literally to express, in some measure at least, the power and poignancy of the original Qur'anic expression, as: 'shall wish that the earth be levelled with them.)
The same wish appears in Suratun-Nisa' where it was said: وَيَقُولُ الْكَافِرُ يَا لَيْتَنِي كُنتُ تُرَابًا
. This will be on the plains of Resurrection when the disbelievers will see that all animals have been turned into dust after having exchanged the retribution of each other's excesses. They too, would pine for an end like this wishing to have become all dust.
Finally, the verse says: وَلَا يَكْتُمُونَ اللَّـهَ حَدِيثًا (And they shall not conceal anything from Allah - 42). It means that these disbelievers will be unable to keep anything about their beliefs and deeds concealed from Allah. Their own hands and feet will confess. The prophets will testify and, of course, present there will be everything on record in their Books of Deeds.
Sayyidna Ibn ` Abbas ؓ was asked: "At one place, the Holy Qur'an says: 'And they shall not conceal anything from Allah' (4:42); while, at another place, it says: 'By Allah, Our Lord, we were no mushriks' (6:23) - Is there, as it seems, any contradiction between the two verses?" To this he replied: What will happen is that when the disbelievers will begin to see that nobody except true Muslims is being admitted into the Paradise they would decide to refuse point-blank that they had ever committed shirk or any other evil deed, in the hope that the plan works and results in their salvation. But, soon after this refusal of theirs, the very parts of their body would testify against them, which would totally frustrate their plan to conceal the truth about their deeds. That will be the time when they will confess every-thing. Hence: "They shall not conceal anything from Allah".