Overall meaning : I swear by the planets with their retrograde motion (that hide themselves in the rays of the sun or when they set) which run their courses and then disappear, by the night when its darkness recedes and by the morning when it appears and brightens up that this Qur’an, which has been revealed to Muhammad, is conveyed by Gabriel, a messenger who is honoured by Allah, endowed with great strength and held in high honour with Allah—the Lord of the Throne—obeyed by the angels in the heavens and is absolutely faithful to his trust—faithfully delivering the revelations Allah entrusts to him.
Your Prophet Muhammad, whom you, Quraysh unbelievers, have known very well over a considerable length of time and whom you have found to be honest and trustworthy, is by no means mad as you claim. Muhammad did see Gabriel in his natural form in which Allah created him when the latter manifested himself on the highest point above the horizon, in the eastern part of the sky, where the sun rises and things are clearly seen.
He does not grudgingly withhold the Qur’an from people; rather, he is keen to convey it and teach it to all mankind. This Qur’an is not the word of a devil who is expelled from Allah’s mercy and pursued by piercing flaming fires. Where, then, can you go away from this Qur’an, idolaters, despite the clear truth it contains and all the proofs supporting it?! Which other path will you, then, take?!
This Qur’an is nothing but a reminder from Allah Almighty to all mankind, to whomever among you wishes to follow the truth and believe in it. But you will not will to do so unless Allah, the Lord of all the worlds, wills that for you.