Judah’s voluntary sexual misbehavior contrasts starkly with Joseph’s refusal to sin sexually even under duress. Judah found himself doubly condemned for condemning Tamar for a sin that he had also committed (Gen 38:26); this challenges the conventional sexual double standard commonly observed in antiquity for men and women. The following contrast with Joseph drives home this point further.

Joseph was attractive (39:6); the text does not count relevant whether Potiphar’s wife was. It also does not inform us whether Potiphar had given Joseph a female partner, which might befit Joseph’s rank in the household. It may depend partly on whether most of the some thirteen years Joseph spent in Egypt before his exaltation (37:2; 41:46) was spent in Potiphar’s household or in prison; a mate was likelier in the former circumstance than in the latter. The narrator does not inform us whether Joseph struggled with temptation; it is simply clear that he refused to sin against God and against Potiphar.

If Potiphar was a literal eunuch (the Hebrew designation appears for Potiphar in both 37:36 and 39:1, as if emphatically), the struggle of Potiphar’s probably younger wife would not be surprising (albeit still a case of sexual harassment). The term might simply designate any officer, however (it appears also in 40:2, 7; cf. 1 Sam 8:15; Jer 29:2). In any case, Joseph recognizes that betraying the trust of Potiphar and sinning with his wife would be a sin against God himself (39:8-9). Joseph’s piety contrasts with Judah’s impiety; see further http://www.craigkeener.org/judahs-punishment-in-genesis-38/.