There are many kinds of atheist and certainly many reasons for being one, but overall it consists in a refusal to accept the supernatural, an unwillingness to place faith above the evidence of one's own senses, a resolve to believing nothing without reasonable evidence, and above all a commitment to the existence of which we know and not to the super-existence of our imagination. Atheism is not primarily negative; it is not primarily anti-supernatural -- it is instead primarily pro-existence, pro-reason, pro-evidence.
That by the way is not faith -- it's simply accepting the fact of existence, and our means of knowing it: Existence exists. There it is. Existence itself is its own evidence. Fairies at the bottom of the garden do not exist, and there is no evidence that either they or imaginary friends do.
Existence itself requires no proof -- it is the very fact of existence upon which all proofs are based: Existence exists. There it is. That's where life and consciousness and all explanation begins.
Existence itself requires no explanation -- existence is a self-sufficient primary: it is not a product of a supernatural dimension or of a supernatural being or of anything else or anyone else. Existence is not a why, it's an is.
Existence itself is simply all that exists -- there is nothing prior to it; nothing antecedent to it; nothing apart from it -- and no alternative to it.
Existence exists -- and only existence exists -- and bOth its existence and its nature are irreducible and unalterable.
By contrast, "gods" as traditionally defined are a systematic contradiction of every form of evidence, and every form of valid logical reasoning -- all gods; all forms of supernatural superpower, from Thor to Wotan to Zeus to Io. No valid argument -- no reason -- will get you from existence to non-existence, or from existence to the supernatural, or from existence to a world contradicting existence. No valid method of inference will enable you to leap from existence to a "super-existence," and nor should it be necessary to try.
Faith -- the means by which one tries to reconcile reason and un-reason, existence and non-existence, evidence and the contradiction of evidence -- is not a means of knowledge, it is a method of rejecting knowledge; it is a means of acting against knowledge, against evidence, against existence.
Faith is not reason. "Faith" designates blind acceptance -- acceptance because it is blind; acceptance because it is unreasonable; acceptance induced in the absence of evidence or even (one might say especially) in contradiction to evidence, in opposition to existence -- acceptance induced by feeling in the absence of either evidence or proof.
Faith is not knowledge, it is an alleged short-cut to knowledge which is only a short-circuit destroying the mind.
As Thomas Jefferson affirmed, " Fix reason firmly in her seat, and call to her tribunal every fact, every opinion. Question with boldness even the existence of a God; because, if there be one, he must more approve of the homage of reason, than that of blindfolded fear."
That's my invitation to you this Sunday.
NB: I should say that in this short spiel I've paraphrased from a number of sources, including Bertrand Russell, Ayn Rand and Leonard Peikoff, particularly from Peikoff's book, Objectivism: The Philosophy of Ayn Rand.