The dictionary definition of “Atheist”, as a non-believer in God or Gods, isn’t accurate because anecdotally there seems to be many people who think the doctrinal teachings of religious institutions are cultural-based anachronisms – and so would be labelled “atheist” for not adhering to definitive religious beliefs about deities – yet believe in some higher spiritual power that they cannot define. This type of thought is different from believing that the universe’s purpose and function is completely explicable in terms contained within itself by matter and its interactions.
There are a lot of belief jumps in this sentence: The universe is a purposeless collection of matter that mindlessly configured itself by chance out of nothing, existing in time with causes and effects that had no beginning. A reasonable-minded adherent might be aware of the glaring uncertainties in this position, but state it is more parsimonious to adopt a materialistic concept of reality, than implant a God belief system as an additional layer in the theory. Yet the certainty with which many proponents preach this position as absolute truth, suggests a type of commitment witnessed in religious belief.
An Agnostic would state that the ultimate “why” questions are unanswerable, so from a practical perspective we should just be concerned with the “how” questions. The materialist’s objections to Agnosticism – based on the burden of proof for God being on the proponent – misses the point to an Agnostic who has already ruled-out religious explanations of God, but not higher meaning and purpose to reality. A particularly zealous materialist might overplay the remit of verifiable facts by stating that opinions about ultimate meaning are irrelevant if they are not scientifically falsifiable – ignoring the fact that their own conceptual model for reality contains unfalsifiable conjecture.
My own instinctive opinion is that I believe religions share the same spiritual root, although the core message was often corrupted by the doctrines and institutions that arose. This is my personal version of “spiritual but not particularly religious”. As I am most familiar with Christianity I can be labelled Christian; however I do adopt a filter and select only what resonates with me, mindful that the scriptures were written and edited by early practitioners of the religion; and that the Biblical canon was decided upon by the politics of powerful men in ecumenical councils, rather than being the unadulterated teachings of Christ. Looking back in history, the cruelties that have been perpetrated by professed followers of the religion, represent the antithesis of the message of Christ; for real spirituality – the root of Christianity – is always inspired by love, joy, harmony, peace and reconciliation.