al-Zukhruf

فَاسْتَمْسِكْ بِالَّذِي أُوحِيَ إِلَيْكَ إِنَّكَ عَلَی صِرَاطٍ مُسْتَقِيمٍ

وَإِنَّهُ لَذِكْرٌ لَكَ وَلِقَوْمِكَ وَسَوْفَ تُسْأَلونَ

43. Therefore, hold you fast to that which is revealed to you. Indeed you are on the Straight Path.
44. And verily this [the Holy Qur’an] is indeed a Reminder [and a Glory] for you and your people and you will be questioned [about it].

One who is on the Right Path benefiting from Divine Revelation is supposed to be assiduous and of lively disposition in his work:

and he is supposed to entertain doubts regarding his true beliefs because of people’s oppositions:

Addressing His Noble Prophet (S), God Almighty says unto him:

“O Muhammad (S)! Do not disturb your noble disposition by disbelievers’ persistence in staying in error and the contemptuous words they say about you and hold fast to Qur’anic Verses and Divine Traditions revealed to you by God Almighty and be content that your are certainly on the Straight Path.”

The antecedent of “this” (inna-hu) is the Holy Qur’an in which lie the glory, honor, and the Straight Path for you and your followers. You and your people will be asked about the Holy Qur’an before long on the Day of Resurrection. The Divine Book is full of Wisdom and Beacons of the Path to human felicity and virtue and you will be asked about what you did with Its instructions.