Exodus 21:1-6 (NIV): If you buy a Hebrew servant, he is to serve you for six years. But in the seventh year, he shall go free, without paying anything. If he comes alone, he is to go free alone; but if he has a wife when he comes, she is to go with him. If his master gives him a wife and she bears him sons or daughters, the woman and her children shall belong to her master, and only the man shall go free.
But if the servant declares, ‘I love my master and my wife and children and do not want to go free,’ then his master must take him before the judges. He shall take him to the door or the doorpost and pierce his ear with an awl. Then he will be his servant for life.
In this passage, when an Israelite buys a fellow Israelite as a slave, the slave is to serve a maximum of 6 years. But if he decides to continue to serve his master, then his ear is pierced, then he serves his master for life.
But in order to keep his slave forever, I can see the master giving him a woman as his wife as an incentive, because the passage states that after 6 years of service, the slave would be allowed to go free, but not his wife and his children. So then, the slave, not wanting to be separated from his family, would have no choice but to become his permanent slave.
Is that really what this part of the law means, that a master may permanently enslave someone by giving them a spouse?