Génesis 29:28 Comentario: Chizkuni, Or HaChaim, Radak & Rav Hirsch

ויתן לו את רחל, “he gave him Rachel;” if you were to ask how Yaakov could legally have lived with two sisters, while both were alive, something forbidden by Jewish law, and according to tradition he kept the entire Torah laws, our sages have said that when a pagan undergoes conversion, all previous family relationships are retroactively cancelled (Yevamot 22), so that as soon as Leah became Yaakov’s wife, Rachel automatically had ceased to be her sister. A convert is considered as if a newly born person. An alternate exegesis: Leah and Rachel had been halfsisters sharing only their father. In Jewish law these family ties are dependent on the mother, not the father. Proof of this can be found in Deuteronomy 7,4; from here it is clear that the word בנך, “your son,” is a term that applies only to a son born by a Jewish mother, otherwise he would have been referred to as “her son.”

לו לאשה. As a wife for him. The emphasis on the word לו indicates that Rachel was to be the mainstay of Jacob's household, the עקרת הבית, seeing she was his true mate, בת זוגו.

ויעש...ויתן, Lavan, in accordance with what he had said.