As discussed in the previous mitzvah, a man who acquires a Jewish maidservant is supposed to betroth her or designate her to his son. If this doesn’t happen, he has the alternative of “Plan B,” namely facilitating her redemption by her family. He does this by pro-rating the price he paid for her service and allowing the girl or her family to pay off the balance rather than insisting that she work the full six years that a male would normally work. (And he certainly can’t make a profit by having her redeemed for more than the value of her remaining time!)
The basis of this mitzvah is, once again, compassion for the person whose dire circumstances forced them into servitude. But what if the buyer neither marries her nor assists in her redemption? Ah… read on to the next mitzvah!
The obligation to assist in a servant girl’s redemption only applies to men and only at a time when the Jubilee year is observed. It is found in Talmud Kiddushin 19 and in Mishneh Torah Hilchos Avadim chapter 4. It is #234 of the 248 positive mitzvos in the Rambam’s Sefer HaMitzvos.