Allah [may He be Glorified] said: "An insight and a Reminder for every slave who turns to Allâh (i.e. the one who believes in the Oneness of Allâh and performs deeds of His obedience, and always begs His pardon)" (50:8)
This verse came after the following two verses: "Have they not looked at the heaven above them, how We have made it and adorned it, and there are no rifts in it? And the earth! We have spread it out, and set thereon mountains standing firm, and have produced therein every kind of lovely growth (plants)" (50:6,7) There is an indication to the fact that what is observed in the universe of accuracy and strength are concrete proofs of the perfection of Allah's Might [may He be Glorified].
The wonderful design and creation of the heavens and the earth point out that Allah is the Wisest of all judges and All-Knowing.
Moreover, both the heavens and the earth contain a lot of benefits for the people, which denotes the comprehensiveness of Allah's Mercy and His great Generosity and Grace. They also point out that Allah is the One and Only Master, without Whom all the creatures cannot dispense, He has neither partner (wife) nor child, there is none equal or comparable unto Him. He is the Only One to Whom worship, humiliation and love must be dedicated.
The verse refers to the fact that pondering over these signs gets man out of ignorance and formulates a remembrance of that which benefits the Muslim in his religion and in his world, and of what Allah and His Messengers brought to us. The above-mentioned results however cannot be achieved except through repentance to Allah, by having sincere love for Him, fearing His punishment, wishing for His reward and responding to the invitation of His Messengers. As for those who turn away from contemplating these verses, then neither proofs nor warners benefit those who believe not.
See Tafsir Ibn Sa'di, p.747. (Al-Luwaihiq Edition).