What does Genesis 24:37 mean?

Abraham's servant has described the wealthy status of Abraham and his unmarried son Isaac, living in Canaan. Now he begins to describe the circumstances around his visit to Nahor, the town, and Nahor's extended family.

He starts by answering the obvious question: Why has Isaac not married a local girl? The servant's oath answers the question: Abraham forbids it. Isaac must not marry any of the women in Canaan. This was an issue of culture and spirituality for Abraham, not one of race. His concern was about mixing the godless approach of the Canaanites with that of his family. Later, this prohibition would become an official part of God's law for the people of Israel (Deuteronomy 7:1–4).

Rebekah's family will not likely understand Abraham's concern about Isaac marrying a Canaanite and losing his unique identity among the people there, but they will grasp the point that, for Isaac, the local women are not eligible.