There are three things, according to the Quran about which there is no doubt. They are the existence of God, the Day of Judgment, and the holy Quran.
The holy Quran negates all doubts concerning three things: God, the Day of Judgment, and the Quran itself.
1. There is no doubt that a Wise Being created this awe-inspiring universe. From a single cell in our body to the solar system, from a small insect to the planet Earth, from our eyelashes to high mountains, everything speaks loudly of a Wise Designer. Can all this be a haphazard and accidental harmony? Absolutely not. That is why the holy Quran says,
Is there any doubt about God, the Originator of Heaven and Earth? (14:10)
2. There is no doubt that there will be a day when human beings, as agents possessing free will, will be judged and rewarded or punished based on their deeds; otherwise, the whole system of creation would be meaningless. How many righteous and virtuous people die in misery and how many evil and wicked people die in affluence. Without the Day of Resurrection, why would one do good deeds and refrain from bad deeds? Why would one give his or her money to charity?
Referring to this plain logic, aside from other reasons, the Quran says,
God: There is no god but He. He will gather you together on the Day of Resurrection which is certain to come; and whose word is truer than God's? (4:87)
3. Unlike previous scriptures, there is no doubt in veracity of the Quran, the last and the everlasting divine scripture. This fact is referred to in the Quran, as well, where it says,
This is the Book, there is no doubt in it, a guidance to the God wary. (2:2)
Now, some may say: How can we be sure the Quran is from God? The Quran has already answered to that. Fourteen centuries ago it announced,
If you (all) are in any doubt about what We have sent down to Our servant, then bring a chapter like it and call in your witnesses besides God if you are so truthful. If you do not-and you will never do so-then heed the Fire which has been prepared for disbelievers whose fuel is mankind and stones! (2:23-24)
As you may know, until today, no one has taken up this challenge.