It was revealed in Mecca, it is thirty passages long, consisting of three hundred and thirty words and one thousand three hundred letters. (Tafsir Al-Khateeb Al-Sharabini Vol .3 P.367.)
Ibn Shihab said that is it known as 'the disputer' as it disputes with those of the grave! (Ibid) Those of the grave meaning the two angels Munkar and Nakir who question the servant after they are buried and their relatives have gone.
All of the Quran is blessed and parts of the Quran we have been informed about their specific blessing and others we have not. One such Surah that we have been informed about its blessing is Surah Mulk.
Notice that death comes first as this is much harder to deal with its consequences than life. When death comes it takes us out of our comfort zones as it scares us into considering our mortality. Life can be a trail for parents who do not wish to have children. They worry about provision and other unnecessary concerns.
When you ponder these meanings then you begin to think about the ephemeral nature of life and then you begin to contemplate the afterlife.
There are many hadith explaining its qualities and its benefits we shall go through some.
Ibn Abbas (may Allah be pleased with him) narrated that the Messenger of Allah (may Allah bestow peace and blessings upon him) said, “I wish that “Blessed is the Dominion” would be in the heart of every believer.” (Al-Hakim in Al-Mustadrak 1/253 and Qurtabi in his commentary 17/205.)
This does not just mean that we memorize it verbatim but are heedless of its meanings. Learn the meanings as well, then when you recite it you go over the meanings thus increasing your attendance in the prayer.
Abdullah Ibn Mas’ud (may Allah be pleased with him) said, “When the deceased are placed in their grave; it comes in front of his legs and says, “There is no way for you here as he used to perform the Surah Al-Mulk.” Then it would stand before his head and say to his tongue, “There is no way for you because he used to recite Surah Al-Mulk.” Then he said, “It is protector from the punishment of Allah. It is in the Torah that whoever recites the Surah Al-Mulk has increased and become more fragrant.” (Al-Qurtabi 18/205.)
Ibn Abbas (may Allah be pleased with them) narrates that the Messenger of Allah (may Allah bestow peace and blessings upon him) said, “It is a protector; a rescuer; saving from the chastisement of the grave.” (At-Tirmidhi and Al-Hakim.)
Ibn Mas’ud (may Allah be pleased with him) narrates that the Messenger of Allah (may Allah bestow peace and blessings upon him) said, “Surah Tabaruk protects from the punishment of the grave.” (Ibn Mardawaya.)
The grave is one of the most daunting abodes that someone will enter as it will be as you were, in the world. There is no hiding or pretending in the grave and here, in this place of maggots and worms, it comes to save you. As its recitation will protect us against being punished in the grave as the time in the grave will be longer than the time on earth, it is without comparison.
Ibn Abbas (may Allah be pleased with him) narrates that the Messenger of Allah (may Allah bestow peace and blessings upon him) said, “I have found in the book of Allah a Surah thirty passages long; whoever reads it when he sleeps thirty good deeds are written for him; thirty wrong actions are omitted and he is raised thirty degrees. Allah sends an angel to spread his wings over him and protect him from everything until he wakes up. It is the disputer who argues for it reader in the grave and it is Tabarak alldhi biyadihi l-Mulku.” (Sura Mulk) (Ad-Daylami).
It protects you whilst you sleep which is very important as you are unable to defend yourself at that time but because you read it an angel comes to protect you. Also look at the ninety other blessings that you receive for reading it.