And those who disbelieved ask: "Why was not this Reading revealed to him all at once?" Just because, We have to brace your heart with It, and We have to arrange your life with It gradually.
Disbelievers at the time of Messenger used to ask that why was not this Book revealed to him all at once as explained verses 6: 7; 7: 203 and 17: 93. It is told in verse 17: 106: “And this is a Reading which We have sent down in parts so that you might recite it upon mankind at intervals, and We have sent it down by stages”. Today the Arabic Quran reading Fujjar are not asking such doubts, but by hiding and rejecting Adhikr (the Food, Cloth, and Sight of the human soul), they are following Fujjar books written by pseudo-prophets and hypocrites. They are compared to a dog that will not change its attitude whether it is disturbed or not as explained in verses 7: 175-176. These true disbelievers mentioned in verses 4: 150-151 are hurrying for the 30th pseudo-prophet Antichrist and Doomsday.
Lord has codified the life of Messenger according to the Book. It is commanded to the believer in verse 73: 4 that he has to arrange his life according to the Book. See explanation 2: 254; 7: 26 and 9: 28.