What does Genesis 26:34 mean?

This verse marks a sudden and possibly confusing change of subject. The story jumps suddenly forward to Esau at the age of 40. It is possible, if not likely, that everything up to this point in the chapter, including all of Isaac's dealings with the Philistines in Gerar, took place before Jacob and Esau were born. This is entirely plausible, since Isaac and Rebekah were childless for the first 20 years of their marriage (Genesis 25:20; 25:26). And, very early in their stay in Gerar, they were able to lie about Rebekah being married (Genesis 26:6–11).

Now we return to the stories of Jacob and Esau. As his father Isaac had done, Esau marries at the age of 40. He doesn't appear to have married nearly as well, however. We're told that Esau marries two Canaanite women—Hittites, specifically. His marriages to Judith and Basemath are said to have made life bitter for his parents (Genesis 26:35). This angst is an issue of faith, not of race; the godless practices of the Canaanites will eventually earn them harsh judgment from God (Deuteronomy 7:1–4; 18:9–14).

It's hard not to wonder if Isaac is partially responsible for this outcome. After all, he was aware the great lengths to which Abraham had gone to secure for him a wife from among Abraham's own people (Genesis 24). Surely Isaac understood how important it had been to Abraham that Isaac not marry a Canaanite woman. If Isaac imagined that the covenant promises and blessing of God would flow through Esau, had he failed to invest the time and energy needed to find him a non-Canaanite wife? Or had Esau refused to follow in his father's footsteps? We don't know.