Surat Fussilat, meaning "The Well-Expounded," starts off with a discussion of how the Arabs around the Prophet (SAW) rejected the message he was sent with completely and entirely. From pg. 524 of Thematic Commentary on the Qur'an by Imam Mohammad al-Ghazali (d.1996). Quote edited to include my preferred translation:
The Qur’an warns the Arabs, then as now, that the more they persist in their rejection of God’s universal truth and His Messenger, Muhammad, the more certain it is that they would meet the end of their ancestors, ʿĀd and Thamūd. The surah says: “If they turn away, say, ‘I have warned you about a blast like the one which struck ʿĀd and Thamūd’” (13).
Why were the people of ʿĀd destroyed? "The people of ʿĀd behaved arrogantly throughout the land without any right, saying, 'Who could be stronger than us?'" (15). Why were the people of Thamūd destroyed? “As for Thamūd, We gave them guidance but they preferred blindness, so they were struck by a blast of humiliating punishment for their misdeeds.” (17).
ʿĀd’s ingratitude towards God and their contempt for their fellow human beings, and Thamūd’s deviation from the true path and their preference for falsehood were the causes for their downfall. Other nations that follow in their footsteps shall face a similar fate, because God never allows corrupt works to bear fruit, and a look at the attitude of today’s Arab nations towards Islam can, alas, inspire only pessimism!
The description of what will befall the disbelievers are expounded upon in great detail for the first 3 pages of the surah. In summary, it will not end up good for them. Then, in the fourth page, starting with ayah 30, Allah (SWT) explains the reward of the ones who believe in Allah.
إِنَّ ٱلَّذِينَ قَالُوا۟ رَبُّنَا ٱللَّهُ ثُمَّ ٱسْتَقَـٰمُوا۟ تَتَنَزَّلُ عَلَيْهِمُ ٱلْمَلَـٰٓئِكَةُ أَلَّا تَخَافُوا۟ وَلَا تَحْزَنُوا۟ وَأَبْشِرُوا۟ بِٱلْجَنَّةِ ٱلَّتِى كُنتُمْ تُوعَدُونَ
As for those who say, ‘Our Lord is God,’ and take the straight path towards Him, the angels come down to them and say, ‘Have no fear or grief, but rejoice in the good news of Paradise, which you have been promised.
نَحْنُ أَوْلِيَآؤُكُمْ فِى ٱلْحَيَوٰةِ ٱلدُّنْيَا وَفِى ٱلْـَٔاخِرَةِ ۖ وَلَكُمْ فِيهَا مَا تَشْتَهِىٓ أَنفُسُكُمْ وَلَكُمْ فِيهَا مَا تَدَّعُونَ
We are your allies in this world and in the world to come, where you will have everything you desire and ask for
نُزُلًۭا مِّنْ غَفُورٍۢ رَّحِيمٍۢ
as a welcoming gift from the Most Forgiving, Most Merciful One.’
Ayah 32 uses an interesting word: نُزُلًۭا. This word translates to "a welcoming gift." In Arab culture of the time, guests were highly regarded, even in jahilliyah. نزلا comes from the root of ن ز ل, which means "to descend." انزَلَ translates to "descended," and يَنزِلُ means "descends." نُزُل a noun form of this verb, which when brute-force translated comes out to "there which you descend into." In modern context, نُزُل means a hotel, and at the time of the Prophet (SAW), نُزُل meant the things you presented to guests as soon as they arrived (and descended into your house). It comes before appetizers or the main course, and is not even considered as something nice you do to your guests. It was something that was so mundane — the idea of not serving some light coffee and dates to your guest was completely bizarre.
The usage of that word in the context of paradise is fascinating. In the ayah preceding, Allah promises the believers "everything you desire and ask for." Not some or most of what you desire, but everything. The anteroom of jannah, the cup of water your host gives you upon sitting down, the coffee and dates of jannah will consist of everything your heart desires and everything you ask for. The levels of jannah that the believers will receieve after these will be a bliss that believers cannot even fathom, that cannot even be described in words in a way that we can completely understand. If everything that you desire is the pre-appetizers, then what is the appetizer? What is the main course? What is the dessert of jannah? We cannot even imagine.