Qul nazzalahu roohu alqudusi min rabbika bilhaqqi liyuthabbita allatheena amanoo wahudan wabushra (surah Nahl: 102)

Tafseer Tafheem-ul-Quran by Syed Abu-al-A'la Maududi

(16:102) Tell them, "The Holy Spirit has brought it down piecemeal *103 intact from my Lord so that He may make firm the faith of those who have believed, *104 and to show the Right Way, *105 and to give good news to those who surrender themselves to Allah." *106

Qul nazzalahoo Roohul Qudusi mir Rabbika bilhaqqi liyusabbital lazeena aamanoo wa hudanw wa bushraa lilmuslimeen

*103) The Holy Spirit': `fibril'. Instead of using the name of the Angel who brought Revelation, his title has been deliberately mentioned to warn the disbelievers that the 'Holy Spirit' who brought Revelation, is free from human frailties. He is neither dishonest that he should add something to or take away something from the Message he brought, nor is he a liar and forger that he should invent and state something in the name of Allah. Nor does he suffer from any human lust that he should practise a deceit. He is wholly pure and holy and conveys the Word of Allah intact.
*104) That is, "The fact that Allah sends down His Message piecemeal does not mean that Allah's knowledge and wisdom are defective as you consider because of your folly. Allah sends His Revelations gradually because human intelligence and capacity to grasp are limited and defective which do not let him understand the whole theme at one and the same time and make it firm in his mind. Therefore, Allah in His wisdom conveyed His Revelation piecemeal through the Holy Spirit. He sends a theme gradually and gives its details by and by and uses different methods and .ways to make it plain to human beings so that they might grasp it according to their abilities and capabilities and become firm in their faith and knowledge.
*105) The second practical wisdom of sending down the Qur'an piecemeal was that those Believers, who obediently followed it, should get necessary instructions for the propagation of Islam and the solution of other problems of life at the time when they were actually needed. It is obvious that if those instructions had been sent down before time and at one and the same time they would not have been useful.
*106) The third practical wisdom of not sending down the Qur'an as a whole at one and the same time was to give good tidings and encouragement to the obedient servants who were suffering from persecution and encountering great obstacles because they needed it over and over again. That is why they were assured of ultimate success time and again to fill them with hope to carry on their mission.