What is the meaning of exodus 20 verse 7?

This passage relates to a number of laws and commandments for the people. Verse 21:7 talks about the rights of girl whose a father wishes to sell into slavery. When being sent to her slave owner, she has to be treated with more dignity than a son sold into slavery would be. The following verses talk about the rights of her new owner. If he wishes to have sex with her and is not satified, he must allow her father the chance to buy her back, but in any case can not sell her on to a gentile slave owner.