The spiritual and moral abyss between a son of Avraham and a daughter of Canaan is so profound that any relationship between them remains forever illusive. The son of Avraham must never come under the influence of a Canaanite woman. We see Avraham, however, accepting marriage with an Aramean woman of his land and birthplace. In as much as both of these nations were idolators, what is the distinction between them? The Ran explains that the difference is in their basic character. The Arameans were of a moral and pure character, whose affinity to idolatry was a correctable intellectual deviation. The Canaanites, on the other hand, were morally corrupt, perverted to the very depth of their souls.
Avraham could not aspire to find a morally pure and chaste woman among them, who would be fitting to share the physical and spiritual engenderment of the Jewish people with his son.