“And what have I elucidated? Misery have I elucidated; the origin of misery have I elucidated; the cessation of misery have I elucidated; and the path leading to the cessation of misery have I elucidated. Why have I elucidated this? Because this does profit, has to do with the fundamentals of religion, and tends to absence of passion, to knowledge, supreme wisdom, and nirvana.” – Siddhartha Gautama from the Majjhima Nikaya.
Yes, there are many archaisms to be found in the ancient religions, and learning about them may or may not be useful. But the fact of their existence is no reason to dismiss the sublime brilliance contained in texts such as “The Practice of Dzogchen” by Longchenpa, “The Crest-Jewel of Discrimination” by Adi Shankara, “The Avadhuta Gita” by Dattatreya, “The Fundamental Verses on the Middle Way” by Nagarjuna, or countless others which, taken together, form the great wisdom inheritance of mankind.
Such wisdom characteristically is expressed absent irony and sarcasm and thus perhaps does not appeal to atheists or agnostics. Nevertheless I would ask they give it their sincere attention. It might be most rewarding, and if they find no wisdom therein at least they might be able to straightforwardly express reasons why.