ויהי בשכון, והוא לא שכן במקום עד שהלך אל בית אביו, אלא לפי שהיה כבד במקנה ועם רב אתו, היה הולך למסעיו מעט מעט, עד שמסעיו דומה למשכן. ויהי בשכון, Yaakov did not reside anywhere until he came to his father; however, seeing that he had so many animals and possessions that he moved extremely slowly, it appeared as if he was actually settling down.
וילך ראובן, הלך לאהל בלהה ושכב עמה. וילך ראובן, he went to Bilhah’s tent and slept with her.
פלגש אביו, אשת אביו היתה נקראת פלגש; שראובן חשב כי לא היתה אסורה עליו לפי שהיתה תחלה שפחה ואחר כן לקחה אביו לפלגש והכתוב מעיד עליה שהיתה לו לאשה, כמו שאמר ותתן לו בלהה שפחתה לאשה, והיתה אסורה עליו, כי בני נח נצטוו על העריות כמו שכתבנו, כל שכן בני יעקב, לפיכך נטל ממנו יעקב בכורתו, כמו שאמר, בחללו יצועי אביו, ונתנה בכורתו ליוסף. פלגש אביו, his father’s concubine. Actually, she was his father’s wife, but in Reuven’s view she was no better than a concubine. Reuven did not consider her as out of bounds to him as she had been a slave woman originally, and his father had subsequently taken her to be his concubine. The Torah clearly states that she had become Yaakov’s proper wife in all matters legal. (30,4) As such Bilhah was totally out of bounds to him. Even before the giving of the Torah, the laws of incest governing all of mankind (Noachide laws) included the prohibition of sleeping with one’s father’s wife. (compare our commentary on 20,24) If such legislation applied to all of mankind, how much more so did it apply to the sons of Yaakov. As a result of this trespass Reuven’s status as Yaakov’s legal firstborn was revoked on Yaakov’s deathbed when he publicly announced his unfitness for the title as we also know from Chronicles I 5,1, and his position was given to Joseph instead.
וישמע ישראל, ופירש מן האשה, זהו שאמר "ויהיו בני יעקב שנים עשר" כי לא היה לו עוד בן, והיה פורש כל ימיו מאשה ומדרכי העולם, והתעסק בעבודת האל, זהו שאמר והיה ה' לי לאלהים, ובדרש לא שכב עמה אלא בלבל יצועה, אמר, אם אחות אמי צרה לה, תהא שפחתה צרה לה, עמד ובלבל יצועה: וישמע ישראל, he stopped living with Bilhah as a result of this. The meaning of the line ויהיו בני יעקב שנים עשר, is that from that time on Yisrael had no further children. He no longer slept with any woman for the remainder of his life. In fact, he basically became a recluse, not attending to mundane activities but concentrating on serving G’d directly. This is what he had meant when he said in his vow, that once he would return safely to his father’s house, והיה ה' לי לאלוקים, “the Lord will be my G’d.” According to the Talmud Shabbat 55 Reuven had not actually slept with Bilhah at all, but had only made her bed look slept in, disturbed, to give the impression that intimacy had taken place there. This was a protest against his father not only having spent most of his married life with Rachel, but even now after her death spending his time with Rachel’s maidservant instead of with his mother, with Leah.