If he do not these three unto her - The words express a choice of one of three things. The man was to give the woman, whom he had purchased from her father, her freedom, unless
(i) he caused her to be redeemed by a Hebrew master Exodus 21:8; or,
(ii) gave her to his son, and treated her as a daughter Exodus 21:9; or,
(iii) in the event of his taking another wife Exodus 21:10, unless he allowed her to retain her place and privileges.
These rules Exodus 21:7-11 are to be regarded as mitigations of the then existing usages of concubinage.