John Calvin Commentary Genesis 24:3

"And I will make thee swear by Jehovah, the God of heaven and the God of the earth, that thou wilt not take a wife for my son of the daughters of the Canaanites, among whom I dwell." — Genesis 24:3 (ASV)

That you shall not take a wife. The kind of discipline that was practiced in Abraham’s household is evident here. Although this man was only a servant, yet, because he was placed in authority by the head of the household, his status as a servant did not prevent his being second in command to his master, so that Isaac himself, Abraham's heir and successor, submitted to his guidance.

So great was Abraham's authority and the reverence for him, that when he appointed a servant to act in his place, this servant, by Abraham's mere will or word, could exercise an authority that other heads of households find difficult to retain even for themselves. Isaac's modesty in allowing himself to be guided by a servant is also evident; for it would have been futile for Abraham to make arrangements with his servant if he had not been convinced that his son would be obedient and manageable. This shows how greatly Isaac respected his father, because Abraham, relying on Isaac’s obedience, confidently summoned his servant.

Now, this example should serve for us as a general rule: it is not permissible for children to marry without their parents' consent. Indeed, natural fairness dictates that in such an important matter, children should depend on their parents' will.

Therefore, how detestable is the Pope's cruelty, who has dared to break this sacred bond apart! For this reason, the impulsiveness of young people must be restrained, so that they do not hastily marry without consulting their fathers.