This paper presents a new perspective on Father Mapple and his sermon in Herman Melville’s Moby-Dick. Mapple is the preacher of Whaleman’s Chapel in New Bedford, which Ishmael happens to visit and listens to his sermon on the Book of Jonah of the Old Testament. Different from the traditional interpretations of the sermon, this paper compares it with the original bible text. It shows the clear difference between the two, which can be regarded as the evidence that his sermon is not quite orthodox or Calvinistic. The unique theology of the sermon, this paper asserts, shows the author’s own theology when he wrote the novel. The sermon provides a theological framework of the Pequod as an independent society, which, like Jonah, contains both a great defiance and hatred toward god-like Moby Dick (Captain Ahab) and self-denying obedience toward god-like Ahab (Ishmael and sailors).