Rashi (to Bereishis 30:10) says that Zilpah was younger than Bilhah. Why did Lavan give the younger maidservant to Leah, his older daughter (and vice-versa)?
Rashi (to 30:10): He did that to support his trickery, so that Yaakov should believe that he was marrying Rachel (and not Leah). 1
Rashi: Since it was customary to give the older maidservant to the older daughter.
Since it says that he gave Zilpah "l'Leah," there was no reason to write "Lah"!
Hadar Zekenim: He made Yaakov think that he was giving her to Rachel. 1
However, it says "Lah" superfluously also when he gave Bilhah to Rachel (29:29)! This is difficult.
Why does it say that he gave Zilpah "Shifchah"? It says (29:29) that he gave Bilhah "l'Shifchah"!
Tosfos ha'Shalem (4): Zilpah was very young, and not so proper to serve.
Ohr ha'Chayim: A Midrash teaches that she already was Leah's Shifchah. Rachel and Leah inherited Bilhah and Zilpah from their mother's Kesuvos. 1 "Bito" is extra, to hint to how she had acquired her. "Lavan" is extra, for only he made it seem that it is a gift.
If so, why does it say l'Shifchah regarding Bilhah? (PF)