Tell a Buddhist that Buddha is an atheist and they will reply that he is a non-theist. The proper answer is – what’s the difference? The distinction, for me, is primarily cosmetic. It is more in application than essential belief.
Atheism is a primary stance about the nature of the universe. God does not exist. No sentient entity created the universe or life. These came about through other forces, still in debate. Non-theism is unconcerned with God’s existence. It’s simply a spiritual non-issue. More like, ‘God doesn’t exist, so why waste time on it,’ as opposed to atheism’s ‘God doesn’t exist and it’s my job to prove it to everybody who might listen.’ These amount to the same beliefs substantively, it’s just a matter of how one deals with these beliefs – with a joke or with an argument.
The non-theist might say they are more agnostic, leaving open the question of God, or that gods exist in a provisional but not an absolute way. But if someone is of a spiritual bent, the question of a creator God, especially one who interferes in our lives, is of absolute import. You cannot walk a spiritual path with God as an indifferent maybe/maybe not and who cares anyway. If God is real, then his/her/its existence is the most important question. Therefore, a spiritual non-theist has de facto decided on atheism.
The stance is the difference. Atheists make a big deal out of proclaiming atheism. Non-theists feel the question has been answered and want to move on with their path of self-development. No big deal.
So, an atheist might be disparaging of ‘stupid Christians’ or anyone who believes in God. An atheist enjoys this feeling superiority. (Not all, but most.) ‘Non-theism,’ Pema Chodron said, ‘is realizing that there is no baby-sitter.’ So, you have to be an adult. And part of being an adult is to not condescend those who believe differently.