As Rashi explains, the sons of Leah (Reuven, Shimon, Levi, Yehuda, Yissachar and Zevulun) disrespected the sons of Bilha and Zilpa, the maidservants of Rachel and Leah, respectively, whom Yaakov had married. Leah's sons viewed the maidservants' sons as inferior and "second-class" members of the family, and therefore treated them with scorn and contempt. Yosef made a point of befriending these four beleaguered brothers in an effort to compensate for the mistreatment they suffered at the hands of Leah's sons.
Towards the beginning of Parashat Vayeshev (37:2), the Torah describes Yosef as "na'ar et benei Bilha ve-et benei Zilpa neshei aviv" – "a lad with the sons of Bilha and Zilpa, his father's wives." Rashi explains this phrase as actually describing two features of Yosef's conduct during his teenage years. First, he acted immaturely, as a na'ar, paying inordinate attention to his appearance. In addition, he was "with the sons of Bilha and Zilpa." As Rashi explains, the sons of Leah (Reuven, Shimon, Levi, Yehuda, Yissachar and Zevulun) disrespected the sons of Bilha and Zilpa, the maidservants of Rachel and Leah, respectively, whom Yaakov had married. Leah's sons viewed the maidservants' sons as inferior and "second-class" members of the family, and therefore treated them with scorn and contempt. Yosef made a point of befriending these four beleaguered brothers in an effort to compensate for the mistreatment they suffered at the hands of Leah's sons.
Professor Nechama Leibowitz noted that Rashi's interpretation of this verse sheds light on the otherwise peculiar term neshei aviv ("his father's wives"), with which the Torah here refers to Bilha and Zilpa. At first glance, one might wonder why the Torah found it necessary to identify Bilha and Zilpa, whom it had already introduced and discussed earlier, in Parashat Vayetze (29:24,30; 31:3,9). Furthermore, once the Torah does, for whatever reason, choose to identify them, why does it refer to them as "his father's wives," rather than simply stating, "Yaakov's wives"?
According to Rashi's comments, however, the explanation becomes abundantly clear. Leah's sons taunted Bilha and Zilpa's children because of what they perceived as these brothers' inferior status, resulting from their having been born to the maidservants. Yosef, however, saw Bilha and Zilpa's sons differently, as the children of neshei aviv – his father's wives. Regardless of Bilha and Zilpa's background, they were, after all, married to Yaakov, and hence their children deserved equal standing as members of Yaakov's family. Indeed, as Am Yisrael emerged as a nation, the status given to the tribes of Dan, Naftali, Gad and Asher – the sons of Bilha and Zilpa – was no different from that afforded to the other tribes. Thus, while Leah's sons saw these brothers as sons of maidservants, Yosef saw them as the children of "his father's wives" who were thus to be treated as brothers in the fullest sense of the term.
Very often, the way we treat others depends on which aspects of their character we choose to underscore. All people – like the sons of Bilha and Zilpa – could be looked upon in one of two ways; they can be defined by either their admirable or less admirable qualities. Leah's sons chose to view their brothers in a more negative light, focusing their attention on Bilha and Zilpa's humble origins. Yosef, by contrast, looked at Dan, Naftali, Gad and Asher and saw full-fledged brothers, young men born to his father and raised in his home. Following the example of Yosef, we are to accustom ourselves to focus our minds on the admirable qualities of our family members and peers, rather than highlighting specifically the aspects of their characters that still require improvement.