What does Genesis 27:42 mean?

Esau was actively planning to murder Jacob after Isaac died. His anger is understandable. Using an elaborate deception in which he pretended to be Esau (Genesis 27:15–17), Jacob had tricked their father into giving him the blessing intended for Esau (Genesis 27:1–5; 27:30–35). This gift was not simply well wishes from dad to son. It was the formal conferring of the blessing of God, for wealth and political rule to one son and not the other. The blessing seems to have been irrevocable and possibly even prophetic (Genesis 27:37).It's not surprising that Jacob's action would threaten his relationship with Esau.

Still, to murder one's brother was no small crime. Fortunately for the intended victim, Esau, he did not keep his plan to himself. He told someone what he planned to do, and the word got back to their mother Rebekah. She, of course, was the one who hatched the plot to deceive Isaac in the first place (Genesis 27:6–10). She immediately tells Jacob about Esau's plan. Interestingly, Rebekah doesn't mention that Esau plans to wait to kill Jacob. Either she didn't know that, or she is afraid that Esau won't be able to hold himself back for long. In either case, the following verse will make clear that she wants Jacob to get out of town right away.

Her description of Esau's heart is interesting. It's a human experience to comfort oneself with a plan to take revenge on those who have hurt us. It's a false comfort that allows us to go about our daily activities until the moment comes when we can act. In that sense, her assessment of Esau's plan is sensible. Then again, one has to wonder what Rebekah thought would happen. She conspired with Jacob to cheat Esau out of his life's most valuable possession! Her punishment for that will be played out over the next few passages. Once her favorite son flees, he won't return until after her own death (Genesis 35:27; 49:31).