John Gill Commentary Genesis 34:9

"And make ye marriages with us; give your daughters unto us, and take our daughters unto you." — Genesis 34:9 (ASV)

And make ye marriages with us
There was no objection on their side, it lay on the other; Abraham's servant was charged by him not to take a wife of the Canaanites to his son Isaac; and the same charge was given Jacob by Isaac, (Genesis 24:3) (28:1) ; and therefore Jacob would never agree that his children should marry any of that nation; and marriages with them were afterwards forbidden by the law of Moses, (Deuteronomy 7:3) ;

[and] give your daughters to us, and take our daughters to you ;
for though at present there were no other daughters in Jacob's family, yet there might be hereafter; and the request is, that for the future there might be intermarriages between them, as would be practicable in a course of time.