Anas bin Malik (RA) narrates that the Prophet (sallallahu ‘alayhi wa sallam) said, “I wish I could see my brothers."
The Companions asked, "Aren’t we your brothers O Prophet of Allah?"
He replied, "No, you are my Companions. My brothers are those who come after me and believe in me without seeing me.” [Ahmad]
What the hadith seems to imply is this. Those of us who have believed in the Messenger of God without actually having seen him, heard his sermons firsthand, and observed his countless miracles- we have a special station in Islam, and a special quota of the Prophet's (and hopefully God's) love. In other words, believing without seeing him, on the basis of relatively less evidence, is in some way more virtuous.
To my mind, this is the hadith where this idea emerges most explicitly, but the theme deeply permeates all of Qur'an and Sunnah. The second chapter of the Qur'an opens with a brief description of the pious, and foremost among these qualities is their belief in the unseen. To some, this seems to fly in the face of common sense- why would believing with less evidence be more virtuous? Why would believing in the unseen be more virtuous than believing in the seen? In this post, I defend the claim that in most circumstances of life, be they religious or secular, believing with relatively less evidence is in fact eminently more virtuous than believing with relatively more evidence. And I think this applies even for scientific truths. The italics may clue you in to the fact that relatively is the key word here. I'm not promoting a generalized (much less universalized) epistemological "less is more" slogan. Sometimes less evidence is indeed less, and believing on the basis of less evidence is bad practice. All I'm saying is- believing on the basis of a degree of evidence relatively lower than a specified higher degree of evidence is good epistemological practice, and therefore more virtuous.
Let me first provide an example which I believe succinctly captures the point. According to this brief news article, Senator Inhofe showed a snowball as an alleged evidence against global warming. Now keeping aside the politics and other ulterior motives this man may or may not have, epistemologically speaking- where do you think Inhofe is coming from? He seems to be saying that were global warming real, this snowball wouldn't have existed. There would be no snow at this time of year. There would be blatant signs of global warming, like people's life getting very difficult due to the heat, no snow or ice outside, temperature reaching all time highs, and so on. So what Inhofe seems to be demanding is- more evidence for global warming! Clearly, the evidence for global warming is found not in any blatant sign in nature like all the snow spontaneously disappearing, but in the published and peer-reviewed scientific literature. A blatant and obvious evidence for global warming would carry more evidential weight than the data on weather patterns and so on that scientists have produced, relying on some (entirely reasonable) assumptions like inferences to the best explanation, induction, and so on. To appreciate and believe on the basis of this latter kind of evidence, there would be more epistemic effort involved, more steps of reasoning to be taken. On the other hand, believing in global warming on the basis of all the snow spontaneously melting would not consider any such extended, rigorous data analysis. Evidence on the basis of blatant perception is clearly of a higher epistemic weight than evidence based on scientific inference (note that I'm not saying scientific inference is "bad evidence"- just that it has lesser epistemic weight than direct perception-based evidence, which should be uncontroversial).
And yet, would anyone think him reasonable? Absolutely not. Even from an epistemological point of view, what this person did was very bad practice. Instead of looking at the countless published papers on the topic, talking sincerely with the experts, analyzing the relevant data thoroughly and so on, he's childishly asking for blatant and near-certain evidences for global warming. In this case, asking for more evidence seems to be simply immature and lazy. In fact, we routinely condemn demands of this sort, especially in science. We look down on some Young-Earth Creationists in their rejection of universalism. The sort of evidence used for for geological dating relies on some intermediate inferences and varieties of induction. For the Young-Earther, this is bad evidence because "you weren't there". It seems obvious that their demand for more evidence in this case is wrong. In fact, I'd go so far as to suggest that this sort of unreasonable demand for extra evidence characterizes all or most science-denialist movements. Clearly, believing on the basis of relatively less evidence isn't always blameworthy, while demanding more evidence sometimes is.
The lesson of this whole discussion is this. In order for a belief to be justified, it needs to be more probably true than false. In other words, when the probability of a belief's being true is 0.51, it becomes justified to hold it. Now that may strike many as cutting a little too close, so feel free to set a reasonable probability value at which a belief gains justification- 0.6, 0.65, maybe even 0.7. When a belief claims a truth-probability around these numbers, however, one becomes justified in holding them, and more importantly, unjustified in not holding them. If one refuses to believe in a proposition that has a, say, 70% probability of being true than false, and demands for more evidence, we characterize that behavior as childish and immature. At and upwards of this minimal probability for justification point, demanding for more evidence becomes unjustified.
This completes the necessary clarification as regards what I meant when I said "less" and "more" evidence. By "less" evidence I didn't mean any arbitrarily low number, to the extent of believing in unjustified propositions. Rather, my "less" is still more than at least the minimal probability for justification point (0.5-0.7). Someone who believes on the basis of this degree of evidence is more reasonable, clear-minded, and epistemologically virtuous than someone who demands for more evidence. This is because the person who believes on the basis of less, but still justifiable degree of evidence, doesn't have the truth of the belief shoved in his face. Unlike beliefs like the existence of the sun, he actually has to reason his way towards the belief, weigh his options carefully, and put in more epistemological effort. Clearly, then, he is more mature and virtuous than the individual who lazily refuses to accept a belief until it becomes so evident that no one has any choice but to believe in it. Remember, we are not afforded any choice in believing in obvious things. You can't believe in the existence of a pink elephant in your room even if I gave you a million dollars. It's easy to see, therefore, why it's more virtuous to believe in something while it's still a choice, as opposed to believing in something when it is shoved in one's face. Indeed, one needs to ask if this latter sort of belief is even virtuous. Is it virtuous at all to believe in the existence of the sun? Would it be at all virtuous to believe in the global warming if and when all ice caps melt and large parts of the world are pulled under the water? But it will definitely be virtuous for someone to read up on the literature now, when the issue hasn't become that obvious, and make a choice to believe in global warming when it's still not very obvious.
This principle clarifies many many aspects about the Qur'an. First and foremost, it tells us why believing in the unseen is a virtue- while the truth of Islam is epistemologically justified, it's not epistemologically certain. It's not as blatantly obvious as the existence of the sun. Believing in it requires effort, and that effort makes it a choice, and that choice makes it virtuous. Second, it explains why the Qur'an is critical of the Qurayshi disbelievers of Makkah who asked for more evidence, despite evidence for Islam being present among them (the Messenger, his miracles and character, and the Qur'an). These and many other concerns related to Divine Hiddenness are clarified once we understand why believing on the basis of less but still justifiable evidence is better than believing on the basis of more evidence.
Finally, consider and contrast the epistemic attitudes of one of the best Muslims to ever have lived with one of the worst disbelievers to ever have lived. Even some of the people who professed Islam had difficulty in believing in the Prophet's night journey, which involved him traveling from Makkah to Jerusalem and back in a single night. From their perspective, in entailing this astonishingly improbable belief, Islam was had some of its epistemic weight subtracted. When told of this miracle, however, Abu Bakr had no difficulty believing in it. His reasoning here is instructive- since Islam entailed believing in even more "out there" propositions- e.g. an angel from God delivering revelation to a man every day- this additional, seemingly less improbable miracle can't change things very much either. It's very interesting that despite the evidential weight of Islam going down after such a miracle's occurrence, Abu Bakr recognized that Islam is still clearly more probably true than false, and hence warrants belief. He didn't complain about the lessening of evidence, because as long as the evidence stayed above the minimal probability for justification point, it didn't matter. He didn't ask for the truth of Islam to be shoved in his face, he believed in it through sound reasoning, and his choice was therefore meaningful and profound. Consider, on the other hand, the equally astonishing miracle of splitting of the moon that happened at the hands of the Prophet in presence of Abu Jahl. This miracle rendered Islam even more probably true than false- perhaps to a point of blatant obviousness. Despite this incredibly high epistemic weight that Islam now carried, Abu Jahl still had the audacity to reject it. For him, while the evidence for Islam is very high, it can still probably be explained by magic. No matter how heavy the evidential weight becomes, Abu Jahl and the other Makkan Qurayshis found grounds to reject them nonetheless, because the truth could be made still more obvious.
Abu Bakr's epistemology resembles that of the careful scientist, while Abu Jahl's one is worse than that of the science-denier.