Allah's statement,

يَوْمَئِذٍ يَوَدُّ الَّذِينَ كَفَرُواْ وَعَصَوُاْ الرَّسُولَ لَوْ تُسَوَّى بِهِمُ الأَرْضُ ...

On that day those who disbelieved and disobeyed the Messenger will wish that they were buried in the earth,

means, they will wish that the earth would open up and swallow them because of the horror of the gathering place and the disgrace, dishonor and humiliation they will suffer on that Day.

This is similar to Allah's statement,

يَوْمَ يَنظُرُ الْمَرْءُ مَا قَدَّمَتْ يَدَاهُ

The Day when man will see that (the deeds) which his hands have sent forth. (78:40)

Allah then said,

... وَلاَ يَكْتُمُونَ اللّهَ حَدِيثًا ﴿٤٢﴾

but they will never be able to hide a single fact from Allah.

indicating that they will admit to everything they did and will not hide any of it.

Abdur-Razzaq recorded that Sa`id bin Jubayr said,

"A man came to Ibn Abbas and said to him, `There are things that confuse me in the Qur'an.'

Ibn Abbas said, `What things do you have doubts about in the Qur'an?'

He said, `Not doubts, but rather confusing things.'

Ibn Abbas said, `Tell me what caused you confusion.'

He said, `I hear Allah's statement,

ثُمَّ لَمْ تَكُن فِتْنَتُهُمْ إِلاَّ أَن قَالُواْ وَاللّهِ رَبِّنَا مَا كُنَّا مُشْرِكِينَ

There will then be no test for them but to say: "By Allah, our Lord, we were not those who joined others in worship with Allah.'' (6:23)

but He also says,

... وَلاَ يَكْتُمُونَ اللّهَ حَدِيثًا

but they will never be able to hide a single fact from Allah.

They have indeed hid something.

Ibn Abbas said,

`As for Allah's statement, ثُمَّ لَمْ تَكُن فِتْنَتُهُمْ إِلاَّ أَن قَالُواْ وَاللّهِ رَبِّنَا مَا كُنَّا مُشْرِكِينَ (There will then be no test for them but to say: "By Allah, our Lord, we were not those who joined others in worship with Allah)'', when they see that on the Day of Resurrection that Allah does not forgive, except for the people of Islam, and that He forgives the sins, no matter how big they are, except Shirk, then the Mushriks will lie. They will say, وَاللّهِ رَبِّنَا مَا كُنَّا مُشْرِكِينَ `("By Allah, our Lord, we were not those who joined others in worship with Allah.''), hoping that Allah will forgive them. However, Allah will then seal their mouths, and their hands and feet will disclose what they used to do. Then, يَوْمَئِذٍ يَوَدُّ الَّذِينَ كَفَرُواْ وَعَصَوُاْ الرَّسُولَ لَوْ تُسَوَّى بِهِمُ الأَرْضُ وَلاَ يَكْتُمُونَ اللّهَ حَدِيثًا (those who disbelieved and disobeyed the Messenger will wish that they were buried in the earth, but they will never be able to hide a single fact from Allah).'''