If he designates her for his son, he shall deal with her as with a daughter.
God gave Israel laws framed in infinite wisdom and equity, not left to human guessing. These were not arbitrary rules but a Theocracy's constitution, suited to make them happy. The Israelites had suffered under Egyptian cruelty; now that they held power over servants, provision was made to ensure they would not replicate that abuse. Those who have felt the whip themselves have no excuse to wield it.
AI summary
Commenting on Exodus 21:1-11
And if he have betrothed her unto his son,.... Not caring to betroth and marry her himself, as being more suitable in age for his son than for himself: he shall deal with her after the manner of daughters; as if she was his daughter, and give her a dowry: or the son shall treat her after the manner the daughters of Israel are treated...
A man who sells his daughter into servitude cannot sell her onward to another master. Either her owner or his son must take her as intended wife with fitting maintenance for her condition, or release her free at once.
AI summary
Commenting on Exodus 21:7-36