Rabbi Ari Kahn
Being married to four women simultaneously can make life complicated. Having children with each of those wives can add to the complications. Having a favorite wife and a chosen child can make life perilous – particularly for that child. This, in a nutshell, was the situation in Yaakov’s home.
The favorite child was Yosef, son of Yaakov's “real" wife Rachel – the only wife Yaakov had ever wanted. Yosef had a rare combination of gifts: good looks, brains, charisma, and a highly developed sense of decency. His brothers oscillated between jealousy and hatred – eventually settling on a combination of the two.
Unlike his brothers, one of Yosef’s “sins” was that he treated the children of his father's pilagshim (concubines) like brothers, which was neither self-evident nor automatic. In families such as this, there is a perceived hierarchy among the wives which carries over to the children, and Yaakov's household was no exception. As Parashat Vayeshev begins, Yaakov's beloved wife Rachel had died in childbirth, leaving two orphaned sons, Yosef and the newborn Binyamin. Yaakov's second wife, Leah, had borne six sons and a daughter; this was the dominant group, both by virtue of strength in numbers and by virtue of their mother's status as a full-fledged wife. The other sons were the children of Bilhah and Zilpah – handmaids of the wives, Rachel and Leah.
Leah's children were intent on establishing their status within the family, now more than ever. Although they could not hope to achieve the preferred status enjoyed by the sons of Rachel, they had no intention of being lumped together with the "second class" children of the concubines, or surpassed by the children of Bilhah, Rivkah's handmaid, who had become a surrogate mother for Rachel's orphaned sons. With this issue of status in mind, Reuven beds Bilhah, at once relegating her to the status of chattel - and by extension, classifying her children as slaves - while at the same time symbolically declaring himself to be Yaakov's true heir.
Yosef's response to Reuven’s gambit is no less clever: Yosef has an affinity for Bilhah, and he defends her honor by honoring her children and treating them as brothers. He counters the outrage committed by Reuven with love toward the secondary victims – the children of the concubines. This becomes a recurrent motif in Yosef’s life: Abuse is repaid with love, never with vengeance. Time and time again, Yosef mends rifts and heals wounds with love.
Yosef's behavior did not arise in a vacuum; he learned it from his father. Yaakov had to contend with his sons' outrageous behavior on more than one occasion: Reuven, and then Shimon and Levi who annihilated the city of Shechem, and more generally the brothers' disdain and rejection of Yosef. Each of these episodes might have served as reason enough for Yaakov to expel one or more of his sons from the family. Had he done so, he would have been following the pattern set in previous generations of the family: Yishmael was banished by his grandparents, and his brother Esav was no longer a part of the clan. And yet, Yaakov does not take this path. He does all that he can (in his own mind, at least) to maintain the unity of the family – and Yosef takes this lesson to heart. Apparently, Yosef understands Yaakov’s silence in the face all the familial intrigue as communicating a basic value: Family first. They must stay together, no matter what. In this spirit, Yosef extends the “family first” attitude to his most vulnerable brothers – the children of the pilagshim.
Not for the last time, Yosef's kindness if repaid with hatred. His brothers detest him; they plot to kill him. Ironically, the conspiracy they hatch to rid themselves of Yosef is what finally unites the other brothers. They share their perfidious secret, and it binds them to one another, forces them to rely on one another for support. The children of the pilagshim could just as easily have used the brothers' dark secret to leverage their own status in Yaakov's household, but they joined the sons of Leah and kept their shared secret to the very end. By remaining silent during and after the sale of Yosef, Bilhah and Zilpah's children become co-conspirators, and Leah's children intuit that the price for their continued silence is a change in the status of the children of the pilagshim. Now, and only now, they become full-fledged brothers, partners in crime, bound by oath to a terrible, unspeakable secret. One wonders if Yosef appreciated the delicious irony: He had succeeded in unifying the family – by becoming the common enemy and victim. We might further wonder whether Yosef actually orchestrated this unity: Although he most probably did not expect them to go as far as they did, perhaps he set himself up as the brother they all loved to hate, allowing them to come together - against him.
This may explain why the hand of God directs Yosef to Egypt. Had he remained with his family, his true greatness could not have emerged. He would have brought himself down to the lowest common denominator for the sake of unity. Yosef could not leave any of his brothers behind – which is why it was so painful when his brothers united to cast him out. Only when he was far away from his family, in Egypt, Yosef’s true personality could emerge, and his greatness become apparent to one and all. His brothers, blinded by jealousy, were unable to see Yosef as he truly was.
 Rashi, Bereishit 37:10.
רש"י בראשית פרשת וישב פרק לז
הבוא נבוא. וַהֲלֹא אִמְּךָ כְבָר מֵתָה, וְהוּא לֹא הָיָה יוֹדֵעַ שֶׁהַדְּבָרִים מַגִּיעִין לְבִלְהָה שֶׁגִּדְּלַתּוּ כְּאִמּוֹ.
 Yaakov sends Yosef to look after his brothers, and encourages him not to separate himself from the others. He reprimands him for his dreams that cause friction and disunity.
 See Rashi, Bereishit 37:2.
רש"י בראשית פרשת וישב פרק לז פסוק ב
את בני בלהה. כְּלוֹמַר וְרָגִיל אֵצֶל בְּנֵי בִלְהָה, לְפִי שֶׁהָיוּ אֶחָיו מְבַזִּין אוֹתָן וְהוּא מְקָרְבָן: