Naming Convention of the Surah* NO.73
This Surah takes its name from the first Ayat, يَا أَيُّهَا الْمُزَّمِّلُ " O you who wraps himself [in clothing]," [73:1].
There are 20 Ayat in this Surah.

Central Theme*
Theme 1: Striving in Ibadah
In the first seven verses the Prophet has been commanded to the effect: “Prepare yourself to shoulder the responsibilities of the great Mission that has been entrusted to you; its practical form is that you should rise during the hours of night and stand up in Prayer for half the night, or for a little more or less of it.”
In v. 8-14, he has been exhorted to the effect: “Devote yourself exclusively to that God Who is the Owner of the whole universe, entrust all your affairs to Him with full satisfaction of the heart. Bear with patience whatever your opponents may utter against you. Do not be intimate with them. Leave their affair to God: He Himself will deal with them.”
Then, in v. 15-19, those of the people of Makkah, who were opposing the Prophet have been warned, so as to say: “We have sent a Messenger to you just as We sent a Messenger to the Pharaoh. Just consider what fate the Pharaoh met when he did not accept the invitation of the Messenger of God. Supposing that you are not punished by a torment in this world, how will you save yourselves from the punishment for disbelief on the Day of Resurrection.”
This is the subject matter of the first section. The second section, according to a hadith from Sa’id bin Jubair, was sent down ten years later and in it the initial Command given in connection with the Tahajjud Prayer, in the beginning of the first section, was curtailed. The new Command enjoined, “Offer as much of the Tahajjud Prayer as you easily can, but what the Muslims should particularly mind and attend to is the five times obligatory Prayer a day, they should establish it regularly and punctually; they should discharge their Zakah dues accurately; and they should spend their wealth with sincere intentions for the sake of God. In conclusion, the Muslims have been exhorted, saying: “Whatever good works you do in the world, will not go waste, but they are like the provision which a traveler sends up in advance to his permanent place of residence. Whatever good you send up from the world, you will find it with God, and the provision thus sent up is much better than what you will have to leave behind in the world, and with God you will also get a much better and richer reward than what you have actually sent up before.”

Connection of the Surah to the Surah before/after it*
In Surah Jinn [72], the listening of the Jinns to the Qur'an was mentioned that how they were influenced when they listened to the Qur'an. In Surah al-Muzzammil [73], the Muslims have been advised to listen and recite it.
Surah al-Muzzammil [73] and al-Mudathir [74] both begin with addressing the Prophet.
Surah al-Muzzammil [73] and al-Mudathir [74] both have similar Ayat speaking of the Qur'an being a reminder
إِنَّ هَـٰذِهِ تَذْكِرَةٌ ۖفَمَن شَاءَ اتَّخَذَ إِلَىٰ رَبِّهِ سَبِيلًا "Indeed, this is a reminder, so whoever wills may take to his Lord a way." [73:19]
كَلَّا إِنَّهُ تَذْكِرَةٌ فَمَن شَاءَ ذَكَرَهُ "No! Indeed, the Qur'an is a reminder. Then whoever wills will remember it." [74:54-55]

Important key and unique words of the Surah*
(73:20) is the longest Ayat of this Surah with 78 words,
إِنَّ رَبَّكَ يَعْلَمُ أَنَّكَ تَقُومُ أَدْنَىٰ مِن ثُلُثَيِ اللَّيْلِ وَنِصْفَهُ وَثُلُثَهُ وَطَائِفَةٌ مِّنَ الَّذِينَ مَعَكَ ۚ وَاللَّـهُ يُقَدِّرُ اللَّيْلَ وَالنَّهَارَ ۚ عَلِمَ أَن لَّن تُحْصُوهُ فَتَابَ عَلَيْكُمْ ۖ فَاقْرَءُوا مَا تَيَسَّرَ مِنَ الْقُرْآنِ ۚ عَلِمَ أَن سَيَكُونُ مِنكُم مَّرْضَىٰ ۙ وَآخَرُونَ يَضْرِبُونَ فِي الْأَرْضِ يَبْتَغُونَ مِن فَضْلِ اللَّـهِ ۙ وَآخَرُونَ يُقَاتِلُونَ فِي سَبِيلِ اللَّـهِ ۖ فَاقْرَءُوا مَا تَيَسَّرَ مِنْهُ ۚ وَأَقِيمُوا الصَّلَاةَ وَآتُوا الزَّكَاةَ وَأَقْرِضُوا اللَّـهَ قَرْضًا حَسَنًا ۚ وَمَا تُقَدِّمُوا لِأَنفُسِكُم مِّنْ خَيْرٍ تَجِدُوهُ عِندَ اللَّـهِ هُوَ خَيْرًا وَأَعْظَمَ أَجْرًا ۚ وَاسْتَغْفِرُوا اللَّـهَ ۖ إِنَّ اللَّـهَ غَفُورٌ رَّحِيمٌ "Indeed, your Lord knows, [O Muhammad], that you stand [in prayer] almost two thirds of the night or half of it or a third of it, and [so do] a group of those with you. And Allah determines [the extent of] the night and the day. He has known that you [Muslims] will not be able to do it and has turned to you in forgiveness, so recite what is easy [for you] of the Qur'an. He has known that there will be among you those who are ill and others traveling throughout the land seeking [something] of the bounty of Allah and others fighting for the cause of Allah. So recite what is easy from it and establish prayer and give zakah and loan Allah a goodly loan. And whatever good you put forward for yourselves - you will find it with Allah. It is better and greater in reward. And seek forgiveness of Allah. Indeed, Allah is Forgiving and Merciful. " (73:20)