Half of it or a little less than that or a little more and...
Half of it or a little less than that or a little more and recite the Qur’an meditatively with utmost clarity and eloquence." It would be of interest to note that the Noble Prophet is herein addressed as: "O you wrapped in garment!" rather than "O Messenger!" or "O Prophet!" reflecting that it would be befitting to rise up, grow spiritually, and prepare oneself for embarking upon such great mission, rather than leading the life of a recluse.
He is urged to rise at night, since his foes are asleep at the time and people desist from following their daily routines, hence further preparedness for meditation and spiritual growth. Likewise, he is urged to recite the Holy Qur’anic Verses, since they include all the required lessons in this respect. Recitation of the blessed Verses is the best means of strengthening one’s faith, steadfastness, fear of God Almighty, and spiritual growth.
The Arabic word tartil denotes "regularity, articulation, and being well-ordered," though it herein implies articulate, eloquent, and meditative recitation of the Qur’anic Verses, reflecting upon their meanings and impacts on one’s life. It goes without saying that such recitation of the Qur’anic Verses may easily lead man toward spiritual growth, moral nobilities, and fear of God Almighty.
Some Qur’an exegetes maintain that establishing canonical prayers is herein intended, since a major part of such prayers lies in reciting Qur’anic Verses. The clause "stand at night" (qum al-layl) is contrasted with "sleeping," though it does not solely denote standing up.
The point is that the different expressions denoting the spans of time spent in nightly vigilance actually implies "choice"; thus, the Noble Prophet (S) is free to choose to stay awake half of the night or sometime more or less, devoting his nightly vigilance to the recitation of the Qur’anic Verses. Firstly, mention is made of all night, except for a little, then the time span is reduced to half of the night and then to less than half.
Some exegetes hold that choosing amongst two thirds, half, and a third of the night is herein intended, as the closing Verse "Your Lord knows that you stand [to pray at night] a little less than two thirds of the night, or half the night, or a third of the night" reiterates the same statement.