كِتَابٌ أُنزِلَ إِلَيْكَ(This is the) Book (the Qur'an) sent down unto you (O Muhammad),from your Lord,فَلَ يَكُن فِي صَدْرِكَ حَرَجٌ مِّنْهُso let not your breast be narrow therefrom,According to Mujahid, Qatadah and As-Suddi, meaning, having doubt about it.It was also said that the meaning here is:`do not hesitate to convey the Qur'an and warn with it,'فَاصْبِرْ كَمَا صَبَرَ أُوْلُواْ الْعَزْمِ مِنَ الرُّسُلِTherefore be patient as did the Messengers of strong will. (46:35)Allah said here,لِتُنذِرَ بِهِthat you warn thereby,meaning, `We sent down the Qur'an so that you may warn the disbelievers with it,'وَذِكْرَى لِلْمُوْمِنِينَand a reminder unto the believers.Allah then said to the world