Is this a great book or what? It's, in fact, the gospel truth. When someone tells you that what they are saying is gospel or the gospel truth, they're saying that their remarks are undeniably true, to be taken on faith and never challenged. Derived from the Old English god spel, "good news," the idiom originated in the 17th century, referring to biblical truths — specifically, the teachings of Jesus and the Apostles. In the 19th century the term became much more inclusive, applying to truth of a more general nature.
Many people go by the book, "acting in strict accordance with the rules." "What book exactly is that?" you might ask. In the 18th century, the British acted properly according to Crocker, Edward Cocker (1631-75), that is, a popular arithmetician whose book was the last word on the subject.
Americans did things according to Gunter, that's Edmund Gunter (1581-1626), a famed English astronomer and inventor.
People today still do things according to Hoyle, Edmond Hoyle (1679-1769) that is, an English writer and one of the first experts on Whist and a number of other card games.
Can you always go by the book? After Hoyle's death, unscrupulous authors used Hoyle's name on their own rulebooks for games which had not been invented. Years later, Crocker's book was shown to have been a forgery. We have long been warned that you cannot judge a book by its cover; perhaps we have to be similarly wary of its author and its contents as well. Science has lain to rest much of the folklore of The Good Book — the Bible that is. There are clearly times when you just have to close the book on things, or better yet, just write your own.