cellio | daf bit: Kiddushin 20

Having discussed how a man acquires a wife, the talmud goes on to discuss how one acquires a Hebrew slave, how the slave acquires his freedom, and how he is to be treated in between. The g'mara on today's daf talks about how he is to be treated. From "because he (the slave) is well with thee (the master)" (Deut 15:16), we learn that the slave must be with -- equal to -- the master: the master cannot eat white bread while the slave eats black bread; the master cannot drink old wine while the slave drinks new wine; the master cannot sleep on a feather bed while the slave sleeps on straw. Hence it was said: whoever buys a Hebrew slave is like buying a master for himself. (20a)

The Hebrew slave goes free in the seventh year (it's not forever). The verse cited here, though, is from the case where at that time the slave says he loves his master and refuses to go -- in that case he remains forever. This decision is entirely the slave's, so while you think you might be acquiring him, and thus taking on the obligation to treat him as one of your household in exchange for his labor, for six years, it could end up being for much longer.