Then Allah says,

وَإِنَّهُ لَحَسْرَةٌ عَلَى الْكَافِرِينَ ﴿٥٠﴾

And indeed it (this Qur'an) will be an anguish for the disbelievers (on the Day of Resurrection).

Ibn Jarir said,

"And verily this rejection will be anguish for the disbelievers on the Day of Judgement.''

He (Ibn Jarir) also mentioned a similar statement from Qatadah.

It is possible that the meaning of the pronoun (it) may also refer to the Qur'an, in which case the verse would mean that the Qur'an and belief in it are a cause of anguish for the disbelievers.

This is as Allah says,

كَذَلِكَ سَلَكْنَاهُ فِي قُلُوبِ الْمُجْرِمِينَ لاَ يُؤْمِنُونَ بِهِ

Thus have We caused it (the denial of the Qur'an) to enter the hearts of the criminals. They will not believe in it. (26:200,201)

And Allah said,

وَحِيلَ بَيْنَهُمْ وَبَيْنَ مَا يَشْتَهُونَ

And a barrier will be set between them and that which they desire. (34:54)