Follow advice like gospel and you're following it as though it was the final word or authority on the matter.
The word gospel comes from the Old English god meaning "good" and spel meaning "news, a story." In Christianity, the term "good news" refers to the story of Jesus Christ's birth, death, and resurrection. Gospel music is heard in church and sung by a gospel choir. Outside of its application to religion, the word gospel is also used to describe an idea or rule that's accepted as undoubtedly true.