וַֽיְהִי֙ בָּעֵ֣ת הַהִ֔וא וַיֵּ֥רֶד יְהוּדָ֖ה מֵאֵ֣ת אֶחָ֑יו וַיֵּ֛ט עַד־אִ֥ישׁ עֲדֻלָּמִ֖י וּשְׁמ֥וֹ חִירָֽה׃
那時,猶大離開他的弟兄們下去,轉到一個名叫希拉的亞杜蘭人那裡。
Rashi
ויהי בעת ההוא AND IT CAME TO PASS AT THAT TIME — Why is this section placed here thus interrupting the section dealing with the history of Joseph? To teach that his brothers degraded him from his high position. When they saw their father’s grief they said, “You told us to sell him: if you had told us to send him back to his father we would also have obeyed you” (Genesis Rabbah 85:2).
Radak
ויהי בעת ההיא וירד יהודה, after Joseph had been sold. The fact that the Torah speaks of וירד, “he descended,” seems to imply that Dotan was situated at a much higher elevation than Adulam. According to a Midrash quoted by Rashi, the word וירד does not refer to a physical descent but to the brothers having demoted Yehudah from his role of their leader as they held him responsible for the debacle with Joseph. They had repented their part in the whole episode, and they accused Yehudah of not having been firm enough. Just as they had listened to him when he told them not to kill Joseph, they claimed that they would have listened to him if he had suggested that they should bring him back to their father. In Bereshit Rabbah 85,2 the whole paragraph commencing with וירד יהודה until the beginning of chapter 39 is considered as not relevant to the story, at least not at this point. Why then did the Torah insert this episode here thereby spoiling our concentration on what would happen to Joseph? According to Rabbi Eliezer the Torah wanted to create a conceptual link between one “descent,” and another “descent.” Rabbi Yochanan justifies the “interruption,” by linking one הכר נא “please identify!” to another הכר נא. Yehudah had deceived his father with these words, whereas Tamar reminded Yehudah that he had been deceived by her and that his assumption that she was a harlot who had become pregnant by her customer was totally unfounded.(compare 37,2 and 38,25 respectively)
Sforno
ויהי בעת ההיא, והמדנים מכרו אותו, [the Torah contrasts the facts with the perception of the facts, i.e. Joseph was alive but the Midianites had sold him. I believe that this is why the author quotes the beginning of this verse without elaborating on it at all. He leaves it to our imagination to fill in this next item in the tragic chain of errors beginning with the fact that Yitzchok had shown more love for Esau. Ed.] at about the same time when Joseph was sold to Egypt at the suggestion of Yehudah who had proposed this instead of bringing him back to his father and had thereby bereaved his father, Yehudah reaped some of the fruit of his ill advised plans, in that the way was paved for him to be bereaved of two of his own sons in due course.