The specific [mention of] "a gnat (ba'ûdatan)" looks to the frequent parabolic use of them by the masters of eloquence (al-bulaghâ') in such expressions as: "Smaller than a gnat." "Stubborner than a gnat." "He asked me for a gnat's brain." "Rarer than a gnat's brain." "The gnat told the bee: Hold on tight and I'll fly off!" "In Allah's sight the world is not equal to a gnat's wing." And so on. It also suggests the flimsiness of their doubts.
The meaning of "something [even] less than that. (lit. what is above, over, or more than) (mâ fawqahâ)" is what is smaller than it in size or what is of higher value according to eloquence, or what is lower in both value and size. Also the phrase infers that small things are more remarkable in the view of eloquence, and more exquisite in [their] creation.
Consider this: the parts of these phrases are like silken threads which being brought together display a fine embroidery.
Now the parts of the sentence "Now, as for those who believe, they know that it is the truth from their Sustainer - whereas those who reject faith say, ' What could Allah mean by this parable?' (Fa-ammâ alladhîna âmanû fa-ya'lamûna annahû al-haqq min rabbihim wa ammâ alladhîna kafarû fa-yaqûlûna mâdhâ arâda Allâh bi-hâdhâ mathalan):"
Consider this: the [conjunction] "Fa- - Now" [expresses] the branching or ramification (al-tafrî') [of this sentence from the previous one], and this indicates an implied proof which yields this sentence with its two parts. That is, [Allah] does not refrain from [propounding] parables because eloquence requires them, and people who are fair-minded know that they are eloquent, true, and Allah's word. While those who obstinately resist them do not know the wisdom [in them], so are hesitant and ask [about them], then deny [them], then they look on them as trifling. Consequently, since the believer is fair-minded he affirms that the parable is Allah's word while because the disbeliever is obdurate, he asks: "What's the use o this?"
Since "as for (ammâ)" expresses condition and necessity, [here] it indi cates that the predicate ["they know that it is the truth"] is the necessary consequence of the subject ["those who believe"]-, that is, the predicate [to know the truth] is characteristic of the subject [those who believe].
The use of "those who believe (alladhîna âmanû)" instead of 'the believers' is a clear indication that belief is the reason they know it is the truth, just as knowing it to be the truth is belief.
And the use of "that it is the truth (annahû al-haqq)" rather than 'that this is [most] eloquent,' although it would have been more apt in this
context, alludes to the [logical] conclusion of their objections, for their purpose is to deny that [the Qur'an] is Allâh's word.