A person can always repent and completely atone for their previous sins, right? In the cases of a penitent ex-follower of Shabbtai Tzvi and a previous "worshipper" of Hindu deities we see that this matter is not so simple.

Rabbi Mordechai Becher, Jewish historian and lecturer, provides us with a remarkable responsum of the Chacham Tzvi (no. 13) and the Noda B'Yehudah (O.C. 2:10) which weigh the individual and communal factors involved in welcoming back such individuals as full members of the synagogue community.