﴿ كِتَٰبٌ أُنزِلَ إِلَيْكَ فَلَا يَكُن فِى صَدْرِكَ حَرَجٌۭ مِّنْهُ لِتُنذِرَ بِهِۦ وَذِكْرَىٰ لِلْمُؤْمِنِينَ ﴾

“A DIVINE WRIT has been bestowed from on high upon thee -and let there be no doubt about this in thy heart-in order that thou mayest warn [the erring] thereby, and [thus] admonish the believers:”

((It is) a Scripture) this Scripture, i.e. the Qur'an (that is revealed unto thee (Muhammad)) that Gabriel brought to you (so let there be no heaviness in thy heart) let there be no doubt in your heart (therefrom) i.e. there can be no doubt about the Qur'an being from Allah (that thou mayst warn thereby) that you may warn the people of Mecca through the Qur'an in order that they believe, (and (it is) a Reminder unto believers).