It is derived from the word kuwwirat in the first verse. Kuwwirat is passive voice from takvir in the past tense, and means "that which is folded up", thereby implying that it is a Surah in which the "folding up" has been mentioned:
The subject matter and the style clearly show that it is one of the earliest Surahs to be revealed at Makkah.
It has two themes: the Hereafter and the institution of Prophethood.
In the first six verses the first stage of the Resurrection has been mentioned when the sun will lose its light, the stars will scatter, the mountains will be uprooted and will disperse, the people will become heedless of their dearest possessions, the beasts of the jungle will be stupefied and will gather together, and the seas will boil up. Then in the next seven verses the second stage has been described when the souls will be reunited with the bodies, the records will be laid open, the people will be called to account for their crimes, the heavens will be unveiled, and Hell and Heaven will be brought into full view. After depicting the Hereafter thus, man has been left to ponder his own self and deeds, saying: "Then each man shall himself know what he has brought with him."
After this the theme of Prophethood has been taken up. In this the people of Makkah have been addressed, as if to say "Whatever Muhammad (upon whom be Allah's peace and blessings) is presenting before you, is not the bragging of a madman, nor an evil suggestion inspired by Satan, but the word of a noble, exalted and trustworthy messenger sent by God, whom Muhammad (upon whom be Allah's peace and blessings) has seen with his own eyes in the bright horizon of the clear sky in broad day light. Whither then are you going having turned away from this teaching?"
Source: Sayyid Abul Ala Maududi - Tafhim al-Qur'an - The Meaning of the Quran
وَإِذَا الْجَنَّةُ أُزْلِفَتْ
عَلِمَتْ نَفْسٌ مَّا أَحْضَرَتْ
فَلَا أُقْسِمُ بِالْخُنَّسِ
إِنَّهُ لَقَوْلُ رَسُولٍ كَرِيمٍ