Jewish law recognizes two types of slaves – Jewish slaves, who effectively sign a long-term contract and go free after six years, and non-Jewish slaves who will remain the property of the owner for life. A Jewish slave owner, however, must get the non-Jewish slave to agree to undergo a conversion process, including circumcision and immersing in the mikveh, and they are then obligated in some of the mitzvot.
The Gemara on today’s daf (=page) discusses the case of a non-Jewish slave, and Rav Nahman quotes Shmuel as teaching that a non-Jewish slave who is purchased from a non-Jew cannot be permitted to touch wine, even if he underwent circumcision and entered the mikveh, since touching it will make it yayin nesekh. This rule remains in effect until we can be sure that their connection with idol worship has ended. How long is that? Rabbi Yehoshua bn Levi is quoted by the Gemara as teaching that we must wait twelve months until we can assume that those traditions have been forgotten.
Rabbenu Tam points out that the statement made by Rabbi Yehoshua ben Levi was not made in explanation of Shmuel’s ruling, since Rabbi Yehoshua ben Levi lived many years before Shmuel. The statement was made with reference to a different halakhah – that a person who cannot convince his slave to accept conversion to Judaism can allow him to live in his house for twelve months in the hope that during that time he will abandon his pagan beliefs and be willing to accept Judaism. If he refuses to do so, he must be sold to a non-Jew. Our Gemara applies the same reasoning to this situation.
Some suggest that we must have the same concerns with regard to a non-Jew who converts – that we cannot allow him to touch wine until we are certain that a significant amount of time has passed and that he has renounced his earlier pagan beliefs. Most of the commentaries reject this comparison, arguing that we must distinguish between someone who converts to Judaism entirely based on his beliefs and free will, as opposed to a slave who has been sold and is required to convert.