Immediately after mentioning Reuben’s immoral act (35:22), the narrator reminds us that Reuben was Jacob’s firstborn through Leah (35:23). This helps explain how Joseph, Rachel’s firstborn who does act more virtuously, later supplants him (49:4). Reuben was undoubtedly quite young at this point and sexual partners outside the camp may have been limited; perhaps exposure to and the assumption of discretion within the household also limited other options within the camp. Bilhah may have also been more available because she was alone in her tent if she could have someone else caring for Benjamin. Bilhah was Rachel’s servant (29:29; 35:25) and Rachel, who had had her own tent separate from Leah’s (31:33), had recently died.
Nevertheless, word leaked out. Reuben may have expected, as firstborn, to inherit Bilhah, his father’s concubine, after his father’s death. Aside from his offense of implicitly presuming upon his father’s decease, however, hearers of this narrative would view lying with one of one’s father’s bed partners as incestuous (Lev 18:8). Perhaps Jacob could have viewed such an action even as dishonoring the memory of his beloved and recently deceased Rachel (cf. 35:25), desecrating her tent if this action occurred there.
We might think the moral of the story is the severe punishment due sexual immorality, except that the punishment here is not so severe after all. Under the not-yet-given law of Moses, the penalty for sleeping with the sexual partner of one’s father was death (Lev 18:8, 29; 20:11); Reuben receives mercy and goes on to play a further role in Genesis, including keeping Joseph from being killed (Gen 37:21-22). Most hearers of the story would not need to be further informed that sleeping with a father’s bed partner was terrible; they would already envision Reuben’s behavior as horrific.
The point then may be more about human depravity and God’s benevolence. The very ancestors of Genesis’s audience, patriarchs of many tribes of Israel, participated in incestuous adultery (Reuben), mass murder (Simeon and Levi), and planned the murder of their brother Joseph, whom God planned as their very deliverer. God did not choose his people because of their great merit or virtue; that remained true in Moses’s time as well (Deut 9:4-8).
The God who made a covenant with Abraham, Isaac and Jacob, is gracious and merciful (Exod 34:6-7). He is the God who chooses people like Isaiah or Simon Peter, who acknowledge their sinfulness when confronted with absolute holiness (Isa 6:5; Luke 5:8). He chooses people like Saul of Tarsus, who had been persecuting his own people (Acts 9:4-5). He saves sinners like myself, who boasted against his existence before my conversion. How can someone read the narratives of Genesis and not recognize that this is the God of our Lord Jesus? This is the God who calls and saves not because of our merit, not because we are good, but because he is good, because he is gracious. Sometimes we idealize biblical characters such as the patriarchs as great heroes; but God, and not the humans he used then or the humans uses today, is the real hero.