SURAH AL-BAQARAH: 26

PART 1

إِنَّ ٱللَّهَ لَا يَسۡتَحۡىِۦۤ أَن يَضۡرِبَ مَثَلاً۬ مَّا بَعُوضَةً۬ فَمَا فَوۡقَهَا‌ۚ فَأَمَّا ٱلَّذِينَ ءَامَنُواْ فَيَعۡلَمُونَ أَنَّهُ ٱلۡحَقُّ مِن رَّبِّهِمۡ‌ۖ وَأَمَّا ٱلَّذِينَ ڪَفَرُواْ فَيَقُولُونَ مَاذَآ أَرَادَ ٱللَّهُ بِهَـٰذَا مَثَلاً۬‌ۘ يُضِلُّ بِهِۦ ڪَثِيرً۬ا وَيَهۡدِى بِهِۦ كَثِيرً۬ا‌ۚ وَمَا يُضِلُّ بِهِۦۤ إِلَّا ٱلۡفَـٰسِقِينَ۔ 

INDEED IT DOES NOT EMBARRASS ALLAH TO USE AS A PARABLE, A GNAT OR WHAT EXCEEDS IT. NOW, AS FOR THOSE WHO BELIEVE, THEY KNOW IT IS THE TRUTH FROM THEIR LORD; WHILE THOSE WHO DISBELIEVE SAY, "WHAT COULD HAVE ALLAH MEANT BY THIS PARABLE?" BY THIS HE LETS MANY GO ASTRAY, AND BY THIS HE MAKES MANY FIND GUIDANCE. BUT HE DOES NOT LET ANYONE GO ASTRAY THEREBY EXCEPT THOSE WHO ARE SINFUL. 

In this verse a doubt raised about the Quran by the non-believers has been mentioned and then answered. They had been saying that had the Quran been the word of Allah, it would not have used examples of creatures as worthless as a gnat or an ant in its parables. The Holy Quran points out that when one is talking about a worthless thing it is completely appropriate to use the example of a worthless object or creature. 

The Quran also says that these doubts only arise in the minds of those whose minds have lost the power of understanding and reason because of their disbelief, while believers do not get such doubts.

From Ma'ariful Quran, by Mufti Muhammad Shafi RE