Before becoming a prophet, Amos was a sheep herder and a sycamore fig farmer. His prior professions and his claim "I am not a prophet nor a son of a prophet" (7:14) indicates that Amos was not from the school of prophets, which Amos claims would qualify him as a true prophet. Amos' declaration marks a turning-point in the development of Old Testament prophecy. It is not mere chance that Hosea, Isaiah, Jeremiah, Ezekiel, and almost all of the prophets given significant coverage in the Hebrew Bible, give first of all the story of their special calling. All of them seek to protest against the suspicion that they are professional prophets, because the latter discredited themselves by flattering national vanities and ignoring the misdeeds of prominent men.
–Wikipedia