إِنَّ لَكَ فِي النَّهَارِ سَبْحًا طَوِيلًا (Surely, in daytime, you have a lengthy work to do... 73:7). The word sabhun, literally means, 'to flow, walk or move about' from which we also get the sense 'of swimming in the water' because when a swimmer swims in the water, he moves about in it freely without any obstruction. Here the word signifies 'long chain of engagements in the day' which refers to multifarious duties to be performed with alacrity, such as educating the people, preaching to them, reforming humanity, performing domestic chores, discharging social responsibilities and moving about to many other tasks and obligations.
The current verse explicates the third point of wisdom as to why night-prayer was enjoined. This relates both to the Holy Prophet ﷺ and the general body of the Muslim community. During the day the Holy Prophet ﷺ as well as other people have a long chain of engagements for which they disperse and move about as explained in the foregoing paragraph. As a result, it is difficult for them to concentrate on their worshipping activity. The night should be reserved for this purpose. A person should sleep according to his need and perform his night-prayer as well.
A Special Note
Jurists have said that the verse under comment confirms that scholars