מדרש על בראשית 37:27

This they shall give (Exod. 30:12). Observe that Israel was so beloved that even their sins brought them considerable benefit. If their sins could do that, how much more so would their meritorious deeds. You find that when Jacob sent Joseph to his brethren, they watched him approach and said to one another: Behold, this dreamer cometh. Come now, therefore, and let us slay him (Gen. 37:19–20). They hurled him into the pit and said: Let us eat and drink, and then we will kill him. After eating and drinking, they were about to say grace when Judah said to them: We are planning to take a life, yet now we would bless God. If we should do this, we would be blaspheming against God and not blessing Him. Because of this Scripture says: And the covetous vaunteth himself, though he condemn the Lord (Ps. 10:3). Come, and let us sell him to the Ishmaelites and let not our hand be upon him (Gen. 37:27). (And they all agreed.)

Another interpretation: "All of the commandment" (Deuteronomy 8:1). If you have began with a commandment, finish all of it. Why? Rabbi Yochanan said, "Anyone who began with a commandment, and afterwards another comes and finishes it, it will be called according to the name of the one who finishes it." From who do you learn [this]? From Moshe. When Israel left Egypt, what is written? "And Moses took the bones of Yosef with him" (Exodus 13:19). All of the people were involved in the plunder and he was taking care of Yosef's bones. He went and stood among the coffins. He called out and said, "Yosef, Yosef, the time has come for the Holy One, blessed be He, to redeem His children. The Divine Presence awaits [you], and Israel and the clouds of glory await [you]. If you will make yourself appear good, but if not, we will be free of your vow." [Whereupon] his coffin immediately stirred, and [Moses] took it and departed. Moshe departed in the wilderness and did not enter the Land. [So] Israel brought in Yosef's bones and buried them. And the commandment was draped upon them, as it is stated (Joshua 24:32), "The bones of Joseph, which the Children of Israel had brought up from Egypt, were buried at Shekhem." Therefore He said to them, "All of the commandment." Rabbi Yannai said, "Anyone who begins a commandment but does not finish it will bury his wife and two of his sons." From who do you learn [this]? From Yehudah, [where it is stated (Genesis 37:26),] "And Yehudah said to his brothers, 'What gain (betsa) etc.?'" They sat to prepare for the bread [and eat their meal]. He said to them, "We are going to kill our brother and then recite a blessing [over the bread]?" As it is stated (Psalms 10:3), "the one that loots (botsea) and blesses reviles the Lord." Hence is it written, "What gain, etc." "Come, let us sell him to the Yishmaelites" (Genesis 37:27). And they listened to him, as he was a king. And had he said to them to bring him back to his father, they would have listened to him. But rather he began with the commandment and did not finish it. Hence one who begins with a commandment should finish all of it. Rabbi Yochanan said, "Anyone who learns Torah but does not fulfill it, it is better for him to have his placenta roll over his face [and smother him], as it is stated (Deuteronomy 8:1), 'guard to keep.'" Rabbi Acha said, "Anyone who guards it to keep it, merits that the holy spirit should descend upon him, as stated (Psalms 89:1), 'A psalm of wisdom (maskil) of Eitan the Ezrachite, etc.' And so [too] did He say to Yehoshua (Joshua 1:8), 'Let not this Book of the Torah cease from your mouth... [and then will you comprehend (taskil)].'" Hence is it written, "to guard to keep."

Another interpretation (of Gen. 37:35): BUT HE REFUSED TO BE COMFORTED. It is simply that our father Jacob said: See, the tribal covenant has been broken! How I have toiled to raise up twelve tribes. Now I see that, since Joseph has gone, behold the very covenant has ceased. All the works of the Holy One correspond to twelve tribes: twelve constellations, twelve months, twelve hours in the day, twelve hours in the night, twelve stones which Aaron wore < on his breastplate >. But now Joseph has gone! Behold, the tribal covenant has been broken. But did Jacob not know how to take a wife and sire a son so that there would be twelve tribes? < He did not do so > simply because he had kept a vow to Laban, as stated (in Gen. 31:50): IF YOU MISTREAT MY DAUGHTERS OR TAKE WIVES BESIDES MY DAUGHTERS, even after their death < …. > What did Laban do? He brought him outside. He said to him (ibid., cont.): THOUGH NO ONE IS WITH US, SEE, GOD IS A WITNESS…. Because of that vow, he was unable to take a wife. When his sons saw that he was complaining so and that he would not accept consolation, they went to Judah and said to him: You have made all this great misfortune for us! He said to them: I said to you (in Gen. 37:26): WHAT PROFIT < IS THERE IF WE KILL OUR BROTHER AND CONCEAL HIS BLOOD >? Now are you saying: What have you done? They said to him: But did we not hearken to you < when > you said (Gen. 37:27): COME, AND LET US SELL HIM TO THE ISHMAELITES? So we hearkened to you. If you had said: Come, and let us return him to his father, should we not have hearkened to you? In that hour, therefore, they arose and expelled him. How is it shown? From what they read on the matter (in Gen. 38:1): JUDAH WENT AWAY.