In the statement فَلَا يَكُن فِي صَدْرِكَ حَرَجٌ appearing in the first verse, the address is to the Holy Prophet . ؓ and he has been told: This Qur'an is the Book of Allah sent down to you. This should not cause any constraint on your heart. The word: حَرَج (haraj) translated here as ` constraint' means that ` you should have no anguish or apprehension in conveying the Qur'an and its injunctions lest people belie it and hurt you.' (As reported from Abu Al-` Aliyah - Mazhari)
The hint given here is that Allah who has sent down this Book on you has also made arrangements that you shall remain protected and that takes care of any anguish on your part. Some commentators have said that ` haraj' or ` constraint on the heart' refers to the constraint experienced by the Holy Prophet ؓ who, because of his affectionate concern for people, felt pain when they would not believe despite having heard the Qur'an and its injunctions. To offset this constraint, the Holy Prophet ﷺ has been told that the duty with which he has been obligated is simply to make the call and convey the message. Once this is done, it is not his responsibility to see who becomes a Muslim and who does not. Therefore, there was no reason for him to be anxious.