The chapter takes its name from the address to the Prophet by Divinity when he wrapped himself in his cloak in awe of the new revelations. It is a very early Makki chapter revealed straight after the first verses of Sura Al Alaq and Sura Al Qalam.
The first nine verses establish the awesomeness of the night vigil continuing to tell the Prophet not to worry about those who deny him as Allah will deal with them on the day of Accountability.
A graphic picture of the day of judgement follows with the shaking of the mountains and the tearing of the skies which would age children.
The last verse removes the obligation of the night vigil, enjoining amongst other things the establishing of salaa and giving zakaa.