أَوَلَمْ يَكْفِهِمْ أَنَّا أَنْزَلْنَا عَلَيْكَ الْكِتَابَ يُتْلَى عَلَيْهِمْ إِنَّ فِي ذَلِكَ لَرَحْمَةً وَذِكْرَى لِقَوْمٍ يُؤْمِنُونَ ﴿۵۱﴾ قُلْ كَفَى بِاللَّهِ بَيْنِي وَبَيْنَكُمْ شَهِيدًا يَعْلَمُ مَا فِي السَّمَاوَاتِ وَالْأَرْضِ وَالَّذِينَ آمَنُوا بِالْبَاطِلِ وَكَفَرُوا بِاللَّهِ أُولَئِكَ هُمُ الْخَاسِرُونَ ﴿۵۲﴾ وَيَسْتَعْجِلُونَكَ بِالْعَذَابِ وَلَوْلَا أَجَلٌ مُسَمًّى لَجَاءَهُمُ الْعَذَابُ وَلَيَأْتِيَنَّهُمْ بَغْتَةً وَهُمْ لَا يَشْعُرُونَ ﴿۵۳﴾ يَسْتَعْجِلُونَكَ بِالْعَذَابِ وَإِنَّ جَهَنَّمَ لَمُحِيطَةٌ بِالْكَافِرِينَ ﴿۵۴﴾ يَوْمَ يَغْشَاهُمُ الْعَذَابُ مِنْ فَوْقِهِمْ وَمِنْ تَحْتِ أَرْجُلِهِمْ وَيَقُولُ ذُوقُوا مَا كُنْتُمْ تَعْمَلُونَ ﴿۵۵﴾

﴾51﴿ Awa lam yakfihim annaaa anzalnaa 'alaikal kitaaba yutlaa 'alaihim; inna fee zaalika larahmatanw wa zikraa liqawminy yu'minoon
﴾52﴿ Qul kafaa billaahi bainee wa bainakum shaheedaa; ya'lamu maa fis samaawaati wal ard; wallazeena aamanoo bil baatili wa kafaroo billaahi ulaaa'ika humul khaasiroon
﴾53﴿ Wa yasta'jiloonaka bil'azaab; wa law laaa ajalum musammal lajaaa'ahumul a'zaab; wa la ya'tiannahum baghta tanw wa hum laa yash'uroon
﴾54﴿ Yawma yaghshaahumul 'azaabu min fawqihim wa min tahti arjulihim wa yaqoolu zooqoo maa kuntum ta'maloon
﴾55﴿ Yawma yaghshaahumul 'azaabu min fawqihim wa min tahti arjulihim wa yaqoolu zooqoo maa kuntum ta'maloon

﴾51﴿ Is it not sufficient for them that We have sent down to you the Book which is recited to them? Indeed, in this there is mercy and a reminder for a people who believe
﴾52﴿ Say, Allah is sufficient as a judge between us and you. He knows what is in the heavens and on earth. And those who believe in falsehood and deny Allah, they are the ones who are truly the losers
﴾53﴿ And they hasten you for punishment. If it were not for a fixed term of promise, punishment would have come to them. And it will come upon them suddenly while they are unaware
﴾54﴿ They hasten you for punishment, and indeed, Hell will surely encompass the disbelievers
﴾55﴿ On the day when punishment will envelop them from above them and from beneath their feet, and it will be said, Taste the result of what you used to do

[51] This is the second answer to the question. The summary of the answer is that the Qur’an itself is a sufficient miracle and greater than all other miracles, because it is enduring and its miraculous nature is evident to the entire world.
(la-raḥmah) — it is either the cause of Allah’s mercy, or a source of reassurance for the hearts, or "raḥmah" here means a special blessing.
Note: This is a clear proof that miracles are not within the Prophet’s power or control, because the Qur’an is a miracle, and if it had been within the Prophet’s power, then it would have been considered fabrication—just as the polytheists used to object.
[52] This is the conclusion of the previous explanation—that Allah the Exalted has affirmed the truthfulness of the Messenger and the Qur’an, so this is the testimony of Allah Himself, and His testimony is sufficient to establish the truth.
Then, again comes a rebuke to the deniers: that despite this testimony, some put their certainty in false books and baseless doubts, and deny the Book of Allah the Exalted—such a person is in great loss.
[53] This is a rebuke for hastening the worldly punishment, and the response is that the punishment will come at its appointed time and suddenly.
(baghtatan) means that its exact time and date will not be known, even if its signs are present.
[54,55] This is a rebuke for hastening the punishment of the Hereafter (meaning they say it should come before its appointed time).
Then, four terrifying states for the deniers are mentioned: being surrounded by Hell, the overwhelming of punishment, punishment from all directions, and the taste of the punishment.
A similar description has been mentioned earlier in Surah Al-A‘rāf (7:41).