Fundamentally a religion is held together by a vocabulary. The vocabularies of many religions have overlapping meanings or mutually understandable interpretations. This does not mean they are the same but it does mean that today and throughout human history, religions have more or less aimed at similar ideals and goals while also differing about what those are and how to get them. Religion is a top-level meaning which determines the meanings of words (and values, beliefs, etc) beneath it. In this sense, atheism is a religion, scientism is a religion, as are many political movements and sometimes science itself.
For some, gender, sexual, or racial identities are also religious. This shows how strong the power of top-level vocabularies can be in that they can be based simply on physical attributes or imagined ones. It would be good if more people understood that no person knows what God is or what happens after death or what the Buddha meant by never discussing these issues because to describe them is to reify them in ways harmful to experiential religious understanding. I wish more people would see religion as described here because this illuminates religion’s: 1) enormous importance; 2) its ever-present variety; 3) its depths of possibility; and 4) its universal nature. Fundamentally, a human language (with attendant beliefs, values, etc) cannot exist without a religion. ABN