Overall meaning : You, Muhammad, who are wrapped up in your clothes! Stand up in prayer all night, except for a small portion of it. Or pray half the night, or even less than that, or add a little more if you wish―for no blame attaches to you for whatever you choose to do—and recite the Qur’an slowly and very distinctly, making its letters clear.
We will soon send down to you the Qur’an, which is great due to its immense significance and momentous and majestic words that are full of great meanings, as well as weighty in that it contains exacting obligations; it is heavy in the scales of deeds and the unbelievers cannot possibly rebut or challenge it in any way.
Indeed, engaging in the night prayer is heavier and much harder for the worshipper than performing the daytime prayer (as the night is the time for sleep and rest), and more conducive to sounder and more correct recitation on account of the absence of every noise and object which may otherwise distract the mind. During the day, you have abundance of time attending to your different worldly affairs, Muhammad; remember the name of your Lord at all times and devote yourself entirely to His worship. He is the Lord of the East and of the West; there is no god worthy of worship but Him; tale Him, therefore, as the disposer of all your affairs and entrust them to Him alone.