what is right and wrong? how should we treat each other?
You can make compelling universal arguments based on capacity to suffer. Suffering is inherently unpleasant and it morally follows that we ought to avoid inflicting it on others. (As basic and concise as I can be.)
Religion is not a good basis for morality. Look at all of the horrible conflicts and evil actions committed on the basis of religious beliefs. One religion can justify terrorism while another dictates that we must sweep the ground in our walking path to avoid killing insects (Jainist monks).
Also, studies have demonstrated that morality develops thru our upbringing; culture, our parents, peers, schooling, etc. When one reads religious canons, they are picking and choosing concepts that already align with their moral/ethical beliefs. That’s not to say religion can’t play a part in shaping a given culture, which in turn influences the moral development of everyone in that society (including atheists). He’s a good read on this.
An example I like to use for Christians is when God sent two bears to maul and kill 42 children for making fun of Elisha’s bald head. Source
Most Christians would morally disagree with that disproportionate punishment of children. That’s because their moral beliefs are derived from outside of that canon. There’s plenty of other examples (including in the New Testament) in which Christians reject. They are using their existing moral beliefs to interpret the Bible.
why are we here?
Does there really need to be a purpose to our existence? Cosmic chance is a sufficient answer in my opinion.
I understand you were posing those questions to convey why people turn to religion, and I’m not disputing that. I’m disputing the efficacy of religion in actually answering those questions.