The literal method of reading the Scriptures is based on the non-Scriptural conviction that "every sentence in the Bible must be taken literally; whatever the sentence says at the literal level is literally true."
Or, in the words of a bumper sticker: "God wrote it, I read it, that settles it."
Biblical literalism is the first of the five fundamentals of Fundamentalism.
No verse in the Bible says "every verse in the Bible must be read literally." People who adopt this approach to reading the Bible do so on their own authority, not that of the Bible.