The Qur'an did not opt for conciseness by saying something like 'the believers in the Qur'an' (al-mu'minûna bi'l-Qur'ân)\ rather, in order to stud the meaning with subtleties and decorate its appendices with fine points, it preferred "And who believe in that which is revealed to you (wa alladhîna yu'minûna bi-mâ unzila ilayka)." For in "who (alladhîna)" is a sign that the attribute of belief is what is intended, and that a person's other attributes are dependent on it and concealed beneath it.

In the use of the imperfect tense for "(they) believe (yu'minûna)" instead of 'the believers' (al-mu'minûn) [the active participle] which infers [something] being fixed and unchanging, is an indication that belief is constantly renewed on the repeated coming of revelation.

Then with the vagueness of "what (mâ)," it indicates that abbreviated belief is sufficient, and that belief includes exoteric revelation [like the Qur'an] and esoteric revelation like Hadiths.

Concerning "revealed (unzila)," in regard to its matter (mâdda) it indicates that belief in the Qur'an is belief in its revelation by Allâh. Likewise, it means belief in Allâh is belief in Allâh's existence, and belief in the hereafter is belief in the coming of the hereafter.

The use of the perfect tense although the revelation had not yet been completed, is an indication that its completion was as certain as that which had been revealed. Moreover, "(they) believe (yu'minûna)" being in the imperfect tense infers the future, thus compensating for the deficiency inferred by the use of the perfect. Because the Qur'an was revealed in this way [that is, by degrees], you see in its styles that the past very often swallows the future and the imperfect tense dons the attire of the perfect. The eloquence of this is a very subtle:

If a person hears something referred to in the past although it has not yet occurred, it arouses his mind and he is alerted to the fact that he is not alone, but behind him are row upon row at various distances, as though the centuries and their peoples are sitting in tiers rising up behind him. This makes him aware that the address and call directed towards him is being heard by all of them according to its volume. Yes, it is a divine address from which all the rows of men in all the centuries receive their share. Thus, the past is real for most people most of the time, while for a few a little of the time it is metaphorical. So to take the majority into consideration serves better the purposes of eloquence.