Allah, the Exalted, is saying that in the destruction of the disbelievers and the salvation of the believers by us is,
لآيَةً
(a sure lesson). This means an admonition and lesson concerning the truthfulness of that which We are promised in the Hereafter.
إِنَّا لَنَنصُرُ رُسُلَنَا وَالَّذِينَ ءَامَنُواْ فِى الْحَيَوةِ الدُّنْيَا وَيَوْمَ يَقُومُ الاٌّشْهَـدُ
.(Verily, We will indeed make victorious Our Messengers and those who believe in this world's life and on the Day when the witnesses will stand forth.)40:51 Allah, the Exalted, also says,
فَأَوْحَى إِلَيْهِمْ رَبُّهُمْ لَنُهْلِكَنَّ الظَّـلِمِينَ
(So their Lord revealed to them: "Truly, We shall destroy the wrongdoers.) 14:13 Concerning Allah's statement,
ذلِكَ يَوْمٌ مَّجْمُوعٌ لَّهُ النَّاسُ
(That is a Day whereon mankind will be gathered together,) This means the first of them and the last of them. This is similar to Allah's statement,
وَحَشَرْنَـهُمْ فَلَمْ نُغَادِرْ مِنْهُمْ أَحَداً
(And We shall gather them all together so as to leave not one of them behind.) 18: 47
وَذَلِكَ يَوْمٌ مَّشْهُودٌ
(and that is a Day when all will be present.) This means a day that is great. The angels will be present, the Messengers ﷺ will gather and all of the creation will be gathered with their families. The humans, Jinns, birds, wild beasts and domesticated riding animals will all be gathered. Then the Most Just, Who does not wrong anyone even an atom's weight, will judge between them and He will increase their good deeds in reward. Concerning the statement,
وَمَا نُؤَخِّرُهُ إِلاَّ لاًّجَلٍ مَّعْدُودٍ
(And We delay it only for a term (already) fixed.) This means for a fixed period of time than cannot be increased or decreased. Then He says,
يَوْمَ يَأْتِ لاَ تَكَلَّمُ نَفْسٌ إِلاَّ بِإِذْنِهِ
(On the Day when it comes, no person shall speak except by His (Allah's) leave.) This means that on the Day of Judgement no one will speak except with the permission of Allah. This is similar to another verse, which says,
لاَّ يَتَكَلَّمُونَ إِلاَّ مَنْ أَذِنَ لَهُ الرَّحْمَـنُ وَقَالَ صَوَاباً
(they will not speak except him whom the Most Gracious (Allah) allows, and he will speak what is right.) 78:38 Allah also says,
وَخَشَعَتِ الأَصْوَاتُ لِلرَّحْمَـنِ
(And all the voices will be humbled for the Most Gracious (Allah). ) 20:108 In the Hadith about the intercession, which is recorded in the Two Sahihs, the Messenger of Allah ﷺ said,
«وَلَا يَتَكَلَّمُ يَوْمَئِذٍ إِلَّا الرُّسُلُ، وَدَعْوَى الرُّسُلِ يَوْمَئِذٍ اللَّهُمَّ سَلِّمْ سَلِّم»
(No one will speak on that day except the Messengers, and the call of the Messengers will be, "O Allah, save us, save us.") Concerning Allah's statement,
فَمِنْهُمْ شَقِىٌّ وَسَعِيدٌ
(Some among them will be wretched and (others) blessed.) This means that from the people of the gathering (on Judgement Day), some will be miserable and some will be happy. This is as Allah said,
فَرِيقٌ فِى الْجَنَّةِ وَفَرِيقٌ فِى السَّعِيرِ
(When a party will be in Paradise and a party in the blazing Fire) 42:7 Al-Hafiz Abu Ya`la recorded in his Musnad on the authority of Ibn `Umar that `Umar said, "When this verse was revealed,
فَمِنْهُمْ شَقِىٌّ وَسَعِيدٌ
(Some among them will be wretched and (others) blessed.) I asked the Prophet , `O Messenger of Allah, will there be a sign for us to know (which party we are from) Will it be because of something that a person did, or something that he did not do' He said,
«عَلَى شَيْءٍ قَدْ فُرِغَ مِنْهُ يَا عُمَرُ وَجَرَتْ بِهِ الْأَقْلَامُ،وَلَكِنْ كُلٌّ مُيَسَّرٌ لِمَا خُلِقَ لَه»
(O `Umar, it will be due to something that he did and the pens wrote it down. But every easy deed was created for its purpose (to be carried out).) Then Allah explains the situation of the wretched people and the happy people. He, the Exalted, says,