There was no such law yet in force, as the examples of Isaac and Jacob show, who married the daughters of uncircumcised persons; and therefore they do not here reject it as simply unlawful, but only as dishonourable and reproachful.
Related Commentaries of Genesis 34:14
Genesis 34:14
14 And they said unto them, We cannot do this thing, to give our sister to one that is uncircumcised; for that were a reproach unto us: