If s/he is a university professor, chances are the Information in the book is carefully researched. The author has an academic reputation to uphold, and that probably is more valuable to him or her than the success of the book. If the author has no real credentials, and especially if the book is self-published or from a publisher you never heard of, be careful of taking the words to heart.
The nonfiction books with "Druid" in the title fall into two categories: those dealing with the historical, Celtic Druids, and those devoted to neo-druidism.
Druids Celebrate Spring Equinox At Stonehenge
The two categories are completely separate. Neo-druidic books that promise to teach druidism are promoting a philosophy, religion, and lifestyle that was invented in modern times, and uses impressions of ancient druids as its inspiration--like the happy couple to the right.
Look, no one knows what ancient druids believed. They left NO written record, and the writings about them are filtered through Romans and Greeks. Those authors may have been lying, or misinformed, or faithful reporters...we don't know.
That leaves a handful of books by scholars and historians about druids. Of these, I recommend Peter Berresford Ellis' book, The Druids -- or, as Amazon bills it, A Brief History of the Druids (The Brief History). Even though it features Stonehenge on the cover (a construction that preceeds Druids and Celts by a coupla millennia), it's the most recent book that gathers together all that we can know about Druids--from archaeology (including Lindow Man), ancient writing, and Irish and Welsh traditions.
Ellis takes the position that Druids were the educated segment of society--the doctors, lawyers, judges, scientists, and yes, priests. He compares them to the Brahmins of India. He makes conjectures, sifts through the evidence. If you read a book by a different expert, s/he might have different opinions.
Druids are mysterious. They were the elite and guarded secret information. That information died with them, though.
I'm reminded of a line from the book Indeh by Eve Ball--a book about the Apache...a line I can't find right now! Dang. I hope I don't butcher the quote, but one of the Apaches who was telling his history turned to Ms. Ball and said, "You white people, you keep everthing up here in your head, and nothing in your heart."
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