The Quran was sent down so that it could be recited to the people and take them from the darkness of misguidance and ignorance into the light of guidance and wealth of knowledge contained within this noble, profound and completely truthful book. It is by the will of Allah that a person is guided and from darkness to light of the path of Allah which is illuminated and is a straight path as Allah is the most and All praiseworthy. Everything that is contained within the entire heavens and the earth belong to Allah and for the disbeliever as they choose the former temporary life of this world to the eternal permanent life of the hereafter, for them there is profound unhappiness and affliction of the severe punishment and torment that lies in waiting.
The disbeliever preferring this temporary worldly life hinder others from the way of Allah and in their striving appear to make the way of Allah crooked when it is a straight path. Due to their behavior of hindering people from the way of Allah and causing and striving to make it appear as though crooked, this results in them being completely misguided and astray for the path or way of Allah is a just and straight path.
Allah SWT has sent for nation a messenger that spoke in the language of his people to clarify and explain the message of worshipping only Allah and bring them Islam and it is entirely the will of Allah whom he guides and whom he leads astray.
This is entirely dependent on what is sincerely within the hearts of people and the two main causes of being astray are desires and doubts within the people. That is why the Quran a book free from any uncertainty, doubts and contradictions was sent in the Arabic language so that the noble Prophet Muhammad peace be upon him could explain and recite the verses of the Quran to purify the hearts of the people and it is Allah SWT who is the Almighty, All Wise.