Matthew Henry Commentary Genesis 26:34-35

"And when Esau was forty years old he took to wife Judith the daughter of Beeri the Hittite, and Basemath the daughter of Elon the Hittite. And they were a grief of mind unto Isaac and to Rebekah." — Genesis 26:34-35 (ASV)

Esau was foolish in marrying two wives, and still more in marrying Canaanites, strangers to the blessing of Abraham and subject to the curse of Noah. It grieved his parents that he married without their advice and consent. It grieved them that he married among those who had no religion. Children have little reason to expect God's blessing who do what is a source of grief to their good parents.