Kommentar zu Bereschit 39:1

ויוסף הורד AND JOSEPH WAS BROUGHT DOWN — It (Scripture) now reverts to the original subject (and consequently it states ויוסף הורד “Joseph had been brought down to Egypt” before the events last mentioned); it interrupted it only in order to connect the account of the degradation of Judah (Genesis 38:1) with that of the sale of Joseph, thus suggesting that it was on account of him (i.e. Joseph — Judah’s part in the sale of Joseph — ) that they (his brothers) degraded him from his high position. A further reason why this narrative of Judah and Tamar is interpolated here is to place in juxtaposition the story of Potiphar’s wife and the story of Tamar, suggesting that just as this woman (Tamar) acted out of pure motives so also the other (Potiphar’s wife) acted out of pure motives, for she foresaw by her astrological speculations that she was destined to be the ancestress of children by him (Joseph) — but she did not know whether these children were to be hers or her daughter’s (Genesis Rabbah 85:2).

שר הטבחים, he would execute the people sentenced as murderers and would generally be in charge of imprisoned criminals.

ויוסף הורד, whereas Joseph was brought to Egypt against his will, Yehudah, at the same time exiled himself. During that period all the things related earlier had befallen Yehudah. During that period Joseph had been brought to Egypt by the Ishmaelites, the owners of the camels who were also agents acting on behalf of others.