The word: رَّحْمَةٍ (rahmah: mercy) appearing in verse 2: مَّا يَفْتَحِ اللَّـهُ لِلنَّاسِ مِن رَّحْمَةٍ فَلَا مُمْسِكَ لَهَا (Whatever blessing Allah opens for the people, there is none to hold it back,) is general at this place. It includes blessings of one's religion in this world along with those of the Hereafter, such as, faith, knowledge, rightly guided conduct as well as the mission of a prophet and the station of a Waliyy or man of Allah. And it also includes material blessings in the present world, such as, provisions, means, comfort, health, wealth, property, recognition and things like that. The meaning of the verse is quite obvious. It is being said here that the person for whom Allah Ta’ ala intends to open the doors of His mercy, there is no one who can stop it.
Similarly, the second sentence: وَمَا يُمْسِكْ (wa ma yumsik: there is none to hold it back) is general, meaning: what Allah Ta’ ala holds back cannot he released by anyone. This includes hardships and sorrows of the world. Y or example, when Allah intends to shield some servant of His from these, then, there is no one who can dare harass or harm him. And included here is the matter of mercy as well in the sense that, should Allah Ta’ ala decide to deprive a person of His mercy due to some wise consideration of His, then, there is no one who can dare pass it on to him. (Abu Hayyan) Related to this very subject of the verse, there is a Hadith that reports that Sayyidna Mu'awiyah ؓ wrote to Sayyidna Mughirah Ibn Shu'abah ؓ ، his governor at Kufah, asking him to send back to him in writing some Hadith he had personally heard from the Holy Prophet ﷺ . Sayyidna Mughirah ؓ called Rawwad, his chief scribe, in his office and dictated his report as: 'I heard from the Holy Prophet ﷺ ", soon after he finished his salah his recitation of the words: اَللَّھُمَّ لَا مَانِعَ لِمَا اَعطَیتَ وَ لَا مُعطیَ لِمَا مَنَعتَ وَ لَا یَنفَعُ ذَا الجَدِّ مِنکَ الجَدُّ (0 Allah, for that which You give, there is no one to stop, and for that which you hold back, there is no one to give it out, and no efforts by any maker of effort1 works against Your will' ). (Ibn Kathir from Musnad of Ahmad)
And according to a narration of Sayyidna Abu Said al-Khudri ؓ عنہ in Sahih of Muslim, he said these words at the time he raised his head from the (bending) position of ruku' before another sentence: اَحَقُ مَا قَالَ العَبدُ وَ کُلُّنا لَکَ (that is, these words, out of all that a servant of Allah can say, are the most true, incumbent and superior).
Trust in Allah delivers from all hardships
The lesson taught by the cited verse (2) to all human beings is that one should not hope any benefit or fear any harm from anyone other than Allah, instead, one should keep his or her sight trained towards Allah alone. This is the master prescription for a better life in this world as well as in the life to come. This simple antidote delivers one from thousands of anxieties and sorrows. (Ruh-ul-Ma’ ani)
Sayyidna ` Amir Ibn ` Abd Qays ؓ said: Once I get to recite four verses of the noble Qur'an in the morning, I stop worrying about what would happen in the morning and what would happen in the evening. These verses are as follows. The first one is this very verse under study: مَّا يَفْتَحِ اللَّـهُ لِلنَّاسِ مِن رَّحْمَةٍ فَلَا مُمْسِكَ لَهَا وَمَا يُمْسِكْ فَلَا مُرْسِلَ لَهُ مِن بَعْدِهِ (Whatever blessing Allah opens for the people, there is none to hold it back, and whatever He holds back, there is none to release it thereafter - 35:2). The second verse having the same sense appears in Surah al-An'am, 6:17: وَإِن يَمْسَسْكَ اللَّـهُ بِضُرٍّ فَلَا كَاشِفَ لَهُ إِلَّا هُوَ وَإِن يُرِدْكَ بِخَيْرٍ فَلَا رَادَّ لِفَضْلِهِ (And if Allah causes you some harm, no one is there to remove it except He Himself; and if He causes you some good, then He is powerful over everything - 6:17). The third verse is from Surah At-Talaq, 65:7: سَيَجْعَلُ اللَّـهُ بَعْدَ عُسْرٍ يُسْرًا (Allah will soon bring ease after a difficulty). The fourth verse is from Surah Hud, 11:6: وَمَا مِن دَابَّةٍ فِي الْأَرْضِ إِلَّا عَلَى اللَّـهِ رِزْقُهَا (And there is no creature on earth whose sustenance is not on Allah - 11:6). (Narrated by Ibn al-Mundhir, as in Ruh ul-Ma'ani)
And when Sayyidna Abu Hurairah ؓ saw rain falling, he used to say: مُطِرنَا بنوء الفَتحِ (The rain has come upon us through the rise of fath: (the opening) and would, then, recite the verse: مَّا يَفْتَحِ اللَّـهُ لِلنَّاسِ مِن رَّحْمَةٍ (Whatever blessing Allah opens for the people, there is none to hold it back,- 34:2). This term of 'rise of fath' used by him was in rebuttal of the false notion prevailing among Arabs of those days who used to attribute the coming of rains to the rise of particular stars and said that the rains had come upon them through the rise of such and such star. Sayyidna Abu Hurairah ؓ countered it by saying that (the mercy of) rains came to him through (the statement in) the verse of fath or opening. By this, he meant this very verse quoted above. He used to recite it particularly on such occasions. (Reported by Imam Malik in al-Mu'watta)
[ 1] This translation is based on one way of reading this prayer, that is, jidd (with kasrah on the letter jim, but if it is read as jadd, then the correct translation would be: 'no high status of a person may benefit him against Your decree. (Muhammad Taqi Usmani)