The embarrassment of the apostle
First:
Chiefly the apostle was embarrassed for feeling he did not carry out his duty properly; i.e. he feared he did some defect in preaching the religion.
He was tasked to convey the massage, but he feared lest he should have done some negligence about his preaching and conveying the revelation to people.
In other words: he sees that he is responsible about warning people, but he fears he has not warned them properly:
( [O Mohammed, recite this] Book [: the Quran] revealed to you,
and let there be no embarrassment in your breast as to it[s conveyance],
[but only] to warn [the unbelievers and the associaters] thereby, and as an admonition to the believers. )
Chiefly the apostle was embarrassed for feeling he did not carry out his duty properly; i.e. he feared he did some defect in preaching the religion.
He was tasked to convey the massage, but he feared lest he should have done some negligence about his preaching and conveying the revelation to people.
In other words: he sees that he is responsible about warning people, but he fears he has not warned them properly:
( [O Mohammed, recite this] Book [: the Quran] revealed to you,
and let there be no embarrassment in your breast as to it[s conveyance],
[but only] to warn [the unbelievers and the associaters] thereby, and as an admonition to the believers. )
The above between brackets is the explanation of the Quran aya 7: 2
كِتَابٌ أُنزِلَ إِلَيْكَ فَلاَ يَكُن فِي صَدْرِكَ حَرَجٌ مِّنْهُ لِتُنذِرَ بِهِ وَذِكْرَى لِلْمُؤْمِنِينَ