He is a prophet, and he gives us several signs of his power even before he tells us his prophecy. One of the reasons why we know that he is indeed a prophet is from the interpretations that he makes of signs. The signs tell him that the gods do not approve of Creon's behaviour.
Top-left: Wealth worship. The landlord is so impressed and intimidated by the bank note that he barely dares to take it.
Middle-left: Impending doom. You can tell that the narrator is experiencing a sense of upcoming catastrophe through phrases like "I judged that there as going to be a crash." The situation the narrator is in also involves danger: "I must swim across or drown."
Top-right: Rags to riches. Taken literally, this expression means going from the poorest to the wealthiest one possibly can be. But in this context, it is more about 'social riches:' the character goes from being insignificant in the eyes of others, to widely influential.
Middle-right: Wealth worship. The landlord is willing to accept any of the narrator's whims simply because he is wealthy, but at the same time, he fears him and his power: "he hoped he wasn't afraid to trust as rich a gentleman as I was."
Bottom: Impending doom. The threatening danger here is expressed by the fact that a "thin crust" is all that keeps the narrator from falling into the crater.
