Allah tells us what the disbeliever will say on the Day of Resurrection, how they will blame themselves and admit that they wronged themselves in this world. When they see the horrors of the Day of Resurrection with their own eyes, they will be filled with regret at the time when regret will not avail them anything.
وَقَالُواْ يوَيْلَنَا هَـذَا يَوْمُ الدِّينِ
(They will say: "Woe to us! This is the Day of Recompense!") And the angels and the believers will say:
(This is the Day of Judgement which you used to deny.) This will be said to them as a rebuke and reproof. Allah will command the angels to separate the disbeliever from the believers in the place where they are standing. Allah says:
After having shown the possibility and proof of 'Akhirah or Hereafter, Allah Ta’ ala has described some events relating to Resurrection in these verses.
Given in the first verse (19) is the mode in which the dead will rise again. It was said: فَإِنَّمَا هِيَ زَجْرَةٌ وَاحِدَةٌ, it will be only a single [ castigating ] Call and all of a sudden they will begin to see - 37:19). The word: زَجْرَةٌ (Zajrah) is a noun derived from زَجر (zajr), and it is used to carry many meanings in the Arabic language. Out of these, one meaning is: 'To utter such sounds which, when heard by cattle, would motivate them to rise and get moving.' Here, it means the second Sur (Horn or Trumpet) that will be blown by the angel, Sayyidna Israfilll. Hence, it has been expressed as 'zajrah' for the reason that the way some sounds are produced to prompt cattle to rise and get moving, very similarly, this Sur will be blown to make the dead rise.
Though Allah Ta’ ala is, in His infinite power, inherently capable of making the dead rise again without having the صُور Sur blown, yet this صُور Sur will be blown in order to highlight the awe of the Resurrection (Tafsir Kabir). Its effect on the disbelievers has been identified as: فَإِذَا هُمْ يَنظُرُونَ all of a sudden they will begin to see - 37:19), that is, the way they could see in the mortal world, in the same way, they would be able to see there.
Some other commentators have explained it by saying that, overtaken by wonder, they will start looking at each other. (Qurtubi)
Tazkirul Quran
Maulana Wahiduddin KhanOn ayahs 18–25
The universe as we observe from the earth is so complicated and so extensive that the re-creation of human beings in the next world appears to be a work of comparatively smaller magnitude. A greater specimen of the creative power of the Creator is before us, then why should it be impossible for that Creator to engage in creation on a lesser scale? On analysing the human body, it appears that it is a combination of earthly components. Man is made up of substances found on earth, such as water, calcium, iron, sodium, etc. All these are found in our world in abundance, then by utilising the same elements from which He once created human beings, can He not re-create man?
Uthmani text of the Madinah mushaf (King Fahd Complex). Translation: Saheeh International. Tafsir via Quran.com.