NOTES for Gen 39:1-23
Joseph's life is remarkable in that several times he has to start everything from scratch, to begin again after another collapse in life. In Egypt, from the very beginning, in the language of an unbelieving person, he was lucky: he ended up in the household of a court dignitary, where he quickly became steward. Potiphar held one of the highest posts in the Egyptian court hierarchy: he was the chief of Pharaoh's palace guard. It was a responsible position, entrusted to especially trusted persons. The palace guard was both the security service for Pharaoh himself and something like a national guard.
Joseph proved to be a quick-witted man. He quickly understood how to make his master's estates produce the greatest income. Managing such estates was not easy: all of them worked for the market and had to generate revenue. It was the same as managing a large agricultural holding today. Joseph handled it; he managed his master's estates so well that his master concerned himself with nothing "except the food that he ate," as the sacred writer says. It was a career that someone from a nomadic Semitic tribe could not even have dreamed of. Legally, of course, Joseph remained a slave, but his actual position was higher than that of many free Egyptians. In antiquity this was not at all rare, whether in Egypt or in some other countries.
Potiphar probably also had under his command his own special service, something like a special counterintelligence unit, and a special prison where, on the one hand, especially dangerous state criminals were kept and, on the other, high-ranking prisoners. It was precisely in this prison that Joseph eventually found himself. The collapse came unexpectedly and not at all from the direction from which it could have been expected: the story with his master's wife ruined everything. Joseph ends up in prison, but even there he soon becomes a kind of supervisor, something like the senior man among the prisoners.
God, it seems, deliberately does not allow Joseph to settle firmly in the place where it would appear he could spend the rest of his life. He does not allow it because He has His own plan for Joseph.