Tom Woods covers early Christian written sources still kept besides the New Testament.
He starts off with the Didache, also known as the 'Teaching of the 12 apostles". At the time it was highly regarded, and even some people thought it should've been in the new testament, but was only rediscovered in 1873. You can now find all of the documents online to read. The book is about the rules of being a Christian. What to do and what not to do. It emphasizes especially the "golden rule", first love God above all things and treat your neighbor as you would yourself.