Overall meaning : There is no community, Allah warns the unbelievers, which He will not utterly destroy in this world before the Day of Judgement as punishment for their unbelief and denial of His messengers, or subject them to severe chastisement. All this is written in the Preserved Tablet (the Book of the Divine Decrees) and will inevitably come to pass.
Then, pointing out one aspect of His grace which He has conferred upon this Nation, He says: Nothing keeps Us from sending down the miraculous signs that your unbelieving people, Muhammad, seek except that We know they will deny them, just the nations before them disbelieved the miraculous signs they had demanded of their messengers. Allah sent down the miracles they had sought, but then He destroyed them when they stubbornly disbelieved them. Your people, Muhammad, will suffer the same awful fate if they do the same.
He gives the example of the tribe of Thamud, to whom He sent Prophet Salih, peace be upon him: To Thamud We gave the she-camel as a manifest miracle attesting to Our oneness and power and to their messenger’s truthfulness, yet they disbelieved it and so We destroyed them. We send signs only by way of warning people so that they may take heed, believe and desist from their evil deeds
To strengthen His Prophet’s heart and increase his certainty of His help and support, the Almighty says: Remember, Muhammad, when We told you that your Lord encompasses all mankind with His knowledge and power. Convey, therefore, the message entrusted to you and do not be afraid of anyone, for We will surely protect you against them. We only made what We made you physically see during your night journey to Jerusalem and ascension to heaven, as well as the cursed tree mentioned in the Qur’an, as a test for people’s faith so that the believers will be distinguished from the disbelievers. We seek to put fear in their hearts through the punishment against which We warn them, but this only makes them even more stubborn in their unbelief and wickedness.