Honestly I dont know why I belive in a thing that cannot be tested. Perhaps I am not very rational. Perhaps its the divine hand of God intervening. But the answer to this question matters not. The result is the same, pure Faith.
Similarly, I can ask you why you belive in Darwinism, science, and a myriad of other logical reasoning. In other words WHY reality? The answer to this question is a philosophical void, that cannot be filled by science or rationality. But it matters not. You stil continue to function in this world even tho it may be all ficticious.
Of course it's faith. By definition, religion requires faith.
People believe in Darwinism and science because they are conclusions people have come up with using the scientific process. They are the best scientific explanation which people use to describe natural phenomena. As such, they are dynamic in that they can be improved or completely replace need be. Yet science is also not afraid to outright state that they do not know - science doesn't attempt to explain everything, it only attempts to explain what it understands.
Simply because we can't currently explain the metaphysical and philosophical concerns of God and an array of other things does not mean it won't be able to in the future. Those who say that science can never explain something like that are only making predictions based on speculative evidence. What concrete evidence do you have to say that, in the future, we won't be able to do so? One cannot simply reply to this by saying 'its logically that we would not be able to do so', since logic is simply whatever our individual mind thinks is rational. Logic can be wrong - look at the Greeks, everything being made up of 4 elements was logical in their eyes but completely wrong by the standards of today.
As such, science may or may not necessarily lead to a 'void' - one can never really know at the present time. On the other hand, religion does indeed fill this void in human knowledge, but one has to question: with what? It may offer an explanation or better understanding of God but is it the undiluted truth? I'll use Christianity as an example, since its the most common organised religion today. The Bible is at the core of Christianity but from an objective and historic point of view, completely devoid of faith, it does have holes. The Gospels were written atleast half a century after the supposed appearance of Jesus, with the latter two books around one century. Not to mention that these dates may be completely off as well, since the only actual surviving and complete copies of them were several centuries after Jesus' appearance. Ask a historian and they will tell you that there is no hard evidence to concretely prove that Jesus did the things claimed in the Bible - there is speculative evidence but even with this, there are various inconsistencies and inaccuracies. Furthermore, does proving that Jesus existed and did the things he did really prove anything other than him being able to do extraordinary things? Does it really prove the existence of God? What if it's just some guy time travelling and using some futuristic technology to look like he was sent by God? Unless you can prove that the Holy Spirit (God) came down and miraculously made Virgin Mary give birth to Jesus, or likewise with John the Baptist, you can never really know. As such, this is where faith comes in, faith that what the Bible states is true, faith that Jesus did walk the earth and did the things he was claimed to have done, faith that he will come again and so forth. One cannot claim that Christianity is the truth without faith, since from an objective point of view, there is little hard and concrete evidence to say as such. This is much the same as with all other religions.
I truly believe that agnosticism is the only real stance society can adopt. Just as religion cannot concretely prove that there is God, one cannot concretely disprove God. is there actually proof that God does not exist, other than logical reasoning which, as we have already established, is unable to prove something by itself alone? No, there isn't. A lack of supporting scientific evidence for something like God does not mean that there isn't a God, it means just what it's meant to mean - that there is no support evidence. It does not add weight to the argument that God does not exist. This is my greatest annoyance with atheism - they try to use science to develop their argument, when they really shouldn't be. As such, people put science and atheism hand in hand, when they really shouldn't be. Like religion, atheism also requires faith in that there is no God, since as of now, there really is nothing to say as such.
So yeah, I believe that neither religion nor atheism is the undisputed truth. Personally, I would group them together since they are essentially the same in that they both require faith, but I won't since atheists don't see it as such. I respect that people can see religion as being the truth but that's only because they have faith. That said, I can't say the same for atheists. All the atheists I know say that there is no God as well as claim they have no faith, which I reckon is complete bullshit. Religion and atheism attempts to explain the unexplained by offering possible explanations, which becomes truth only to an individual with faith - not the undisputed truth applicable to all individuals. Science and agnosticism is upfront and adopts the stance of 'society currently does not know, it does not attempt to hide our current ignorance of such issues under a veil of being known and understood, even if only partially.