Abu Isa At-Tirmidhi recorded from Ibn 'Abbas that Abu Bakr said, "O Messenger of Allah, verily your hair has turned gray." The Prophet replied,

"Surahs Hud, Al-Waqi'ah, Al-Mursalat, 'Amma Yatasa'lun [An-Naba'] and Idhash-Shamsu Kuwwirat [At-Takwir] have turned my hair gray."

In another narration he said,

"Surah Hud and its sisters.."

In the Name of Allah, the Most Gracious, the Most Merciful.

The Qur'an and its Call to (worship) Allah Alone

A discussion concerning the letters of the alphabet (which appear at the beginning of some chapters of the Qur'an) has already preceded at the beginning of Surat Al-Baqarah. That discussion is sufficient without any need for repetition here.
Concerning Allah's statement,

This means perfect in its wording, detailed in its meaning. Thus, it is complete in its form and its meaning. This interpretation was reported from Mujahid and Qatadah, and Ibn Jarir [At-Tabari] preferred it.

Concerning the meaning of Allah's statement,

This means that it (the Qur'an) is from Allah, Who is Most Wise in His statements and His Laws, and Most Aware of the final outcome of matters.

This means that this Qur'an descended, perfect and detailed, with the purpose of Allah's worship alone, without any partners. This is similar to the statement of Allah, the Exalted,

{And We did not send any Messenger before you but We revealed to him (saying): There is no God but I, so worship Me.} 21:25

It is similar to Allah's statement,

{And verily, We have sent among every Ummah a Messenger (proclaiming): 'Worship Allah (Alone), and avoid Taghut (calling false deities.} 16:36

In reference to Allah's statement,

This means, "Verily, I am unto you a warner of the punishment if you oppose Him (Allah), and a bringer of the good news of reward if you obey Him." This meaning has been recorded in the authentic Hadith which states that the Messenger of Allah ascended mount As-Safa and called out to his near relatives of the Quraysh tribe. When they gathered around him, he said,

"O people of Quraysh, if I informed you that a cavalry was going to attack you in the morning, would you not believe me?"

They replied, "We have not found you to be a liar." He said,

"Verily I am a warner unto you before a severe punishment."

Concerning His statement,

This means, "I am commanding you to seek forgiveness from previous sins and to turn to Allah from future sins, and thereafter you abide by that."

This is in reference to this worldly life.

This refers to the Hereafter, according to Qatadah. "This is like the statement of Allah,

{Whoever works righteousness - whether male or female - while a true believer, verily to him We will give a good life.} 16:97

Concerning Allah's statement,

This is a severe threat for whoever turns away from the commandments of Allah, the Exalted, and rejects His Messengers. Verily, the punishment will afflict such a person on the Day of Resurrection and there will be no escape from it.

This is means your return on the Day of Judgement.

This means that He is capable of doing whatever He wishes, whether it be goodness towards His Awliya' (friends and allies), or vengeance upon His enemies. This also includes His ability to repeat the creation of His creatures on the Day of Resurrection. This section encourages fear, just as the previous section encourages hope.