You probably understand the difference between someone who does believe in God and someone who doesn't - the first likely identifies with a particular religion, and the other is an atheist, right? But what about those who identify as agnostics? If you're like many people on either side of the field, your understanding of agnosticism is a bit sketchy. You may have heard something about agnostics being "on the fence" about God, a generalization that leads to other, more inaccurate generalizations.
Religious types tend to view agnostics with a hint of mistrust and disbelief, as in, "You've heard about how great God is, and you still can't decide whether or not to believe?" Atheists, on the other hand, tend to see agnostics as a wishy-washy sort of non-believer who refuses to definitively declare their non-belief "just in case".
Belief Versus Knowledge
The truth is that true agnosticism has nothing to do with belief, and everything to do with knowledge. Being an agnostic simply means that you understand that God cannot be proven either way - the religious cannot prove that he exists, and the atheists cannot prove that he doesn't. A "strong" agnostic thinks that humans are not capable of proving or disproving the existence of God, and that's just the way it is; "empirical" agnostics acknowledge that we cannot do so now, but we may be able to someday in the future. Agnosticism is simply an understanding that all religions or non-religions are based on belief, and not absolute truths. There are also the pragmatic agnostics, who believe that if there is a God, he doesn't seem too concerned about his creation, so the question is purely an academic one meant largely for debate rather than revelation of divine truths.
Coexistence of Faith and Truth
You can be an agnostic and still be a believer or non-believer - in other words, you may say, "I can't prove that God exists, but I'm pretty sure he does," or "I don't think God exists, but I can't absolutely prove it." Agnostics who believe are called "agnostic theists", and those who don't believe are called "agnostic atheists" - but there's a whole other subset of agnostics who believe we are putting the cart before the horse on this whole God thing. Ignosticists believe that before we can even set out to prove or disprove God, we must first come to a conclusion regarding the definition of God - not a simple thing. Even within your particular church there are probably as many definitions of God as there are parishioners, but the provable definition has to be cohesive, inclusive and exclusive. Belief in God is personal, but proof of God is universal.
The Ancient Question
Agnosticism is as old as religion, and is embraced by some as part of the mystery of faith. The Hindu religion is famous for its agnostic leanings, and the Rigveda is a prime example. In discussing the creation of the universe and the Gods, the Rigveda proclaims, "Who really knows?" - a classic agnostic question and the foundation of the school of thought.
The Greek philosophers founded the school of skepticism based on the understanding that nobody can really prove anything where God or anything else is concerned. That planted the seeds of doubt and curiosity in thinkers from then forward, resulting in the likes of Aristotle, Descartes, Kierkegaard, Kant, Hume, Huxley and Russell, who have all put forward their own philosophies regarding the existence or non-existence of God - or more accurately, why we'll never know or how we could someday find out. Some attempt to deduce the existence of God, but Douglas Adams famously said that if God is faith, proving his existence would cause him to disappear in a puff of logic.