Overall meaning :
Say to the unbelievers among your people, Muhammad, ‘Tell me, if this Qur'an is indeed from Allah and you still deny it, who could be further astray from the truth than you?!’
We will show these unbelievers aspects of Our signs testifying to Our oneness and power in the universe and within themselves until it becomes clear to them that the Qur’an is the truth. Is it not sufficient that your Lord, Muhammad, is witness over everything?!
They are certainly in doubt as to whether they will ever be brought back to life after death and meet their Lord. Surely He encompasses all things: Nothing whatsoever is hidden from Him and absolutely nothing can frustrate His power.