“It is true that God has endowed man with the faculty of reason, which, like a lamp, shows him the right path and dispels his doubts and misconceptions. It is an extremely useful and essential faculty and a great blessing. Nonetheless, it has one major flaw: it cannot, on its own, take us to the level of absolute certainty with respect to the true nature of things, for absolute certainty consists in knowing things as they actually are. The best that reason can do is to postulate the need for something to exist, but it cannot go further and confirm that it does indeed exist. Perfect certainty, whereby we rise from the level of ‘should be’ to that of ‘is’ is only achieved when reason finds an ally that is capable of confirming its speculative reasoning and bringing it into the realm of perceptible facts; and where reason says, ‘it should be,’ this ally is able to confirm, ‘it is.’ As I have already pointed out, reason can only establish the need or requirement for something, and not its actual existence, which are two separate things. Anyhow, reason requires an ally to make up for its imperfect and hypothetical claim of ‘should be’ with the confirmatory ‘is’ by revealing things as they actually are. Hence, the Ever-Merciful and Noble God, who desires to lead man to the level of absolute certainty, has fulfilled this need by providing human reason with many allies. He has opened the path to certainty so that man may not be deprived of his most cherished goal of bliss and salvation, which is only possible through perfect conviction, and so that he may quickly cross the perilous bridge of ‘should be’—which his reason has built on the dangerous river of doubt and conjecture—and reach the impregnable castle of ‘is’ where he finds peace and security.
Reason can have different allies from occasion to occasion, but they are no more than three as far as the limitations of reason allow. To illustrate:
If the testimony of reason relates to perceptible objects that can be seen, heard, smelled or touched, the ally that helps it to reach the stage of certainty is called observation or experience. If the testimony of reason relates to events that happen or have happened in various ages and places, it finds another ally in the form of historical books, writings, letters and other records, which, like observation, bring clarity to the hazy light of reason, such that only a fool or madman will doubt them. If the testimony of reason relates to metaphysical phenomena, which we cannot see with our eyes, hear with our ears, touch with our hands, or substantiate through historical records, then a third ally comes to the aid of reason. This is known as divine revelation.
The law of nature demands that just as reason found allies in the first two instances, it should also find an ally in the third instance, for there is no contradiction in the laws of nature. If God did not desire reason to remain unassisted in knowledge of the sciences and arts—errors and lapses in respect of which are not of much consequence—it would be wrong to assume that he has forsaken man in matters of divine knowledge—which is essential for attaining eternal salvation, and ignorance of which could lead one to hell. It is unfair to think that God has limited the knowledge of the hereafter to notions based on mere conjecture and has not provided any means to verify it, so as to bring certainty to the heart and to confirm that the means for salvation suggested by reason are indeed true and not merely hypothetical.
Having established that in theological matters absolute certainty is only to be attained through revelation, and that man requires perfect certainty for salvation and the preservation of his faith, it becomes obvious that he stands in dire need of divine revelation.
Here it should also be borne in mind that all divine revelations were meant to bestow certainty on man, but the certainty for which the holy Quran has laid the foundations surpasses all past revelations. To elaborate, all divine revelations prior to the holy Quran, being mostly in the form of narratives, only served as testimony to certain events. This is why they became corrupted in the end and selfish and egotistical people interpreted them to suit their own purposes. The holy Quran, however, took upon itself to substantiate its teachings with rational proofs and thus saved man from countless hazards. Firstly, it acted as a true messenger, imparting knowledge of the divine realm; secondly, it substantiated its teachings with the aid of reason.
Anyone who studies the holy Quran will find that, from beginning to end, it provides two kinds of testimonies—the testimony of reason and the testimony of revelation. In the holy Quran these two are like two great streams running in parallel and influencing each other continuously. The stream of reason shows that something ‘should be’, and the stream of divine testimony assures us, like a wise and righteous informant, that ‘it is.’ The advantage of this Quranic approach is obvious, for in reading the holy Quran a seeker finds rational evidence for its teachings—evidence the like of which cannot be found in any work of philosophy. This claim shall also be established in chapter 1 of this book. What is more, he who reads the Quran reaches the highest level of certainty through the testimony of divine revelation and finds in an instant all that others could not find in a lifetime of effort and deliberation. And so we can conclude that the holy Quran alone is the surest, easiest and most perfect means for recognizing the true principles and beliefs upon which our salvation depends.”
-Mirza Ghulam Ahmad, the Promised Messiah and Imam Mahdi (as), Barahin-e-Ahmadiyya Parts 1 & 2, pg.94.