…the talmudic sources are divided. A well known baraita (Yevamot 47a) says that converts should at first be turned away: “Our rabbis taught: If at the present time a man desires to become a proselyte, he is to be addressed as follows: ‘What reason have you for desiring to become a proselyte? Do you not know that Israel at the present time is persecuted and oppressed, despised, harassed and overcome by afflictions?’ If he replies, ‘I know and yet I am unworthy,’ he is accepted immediately ….” After he is accepted, he is instructed in some of the commandments, but his acceptance comes first.
But another source (Bekhorot 30b) insists that a convert who rejects a single iota of Jewish law may not be accepted. These sources can be made to agree, but doing so clouds the question that their apparent contradiction raises. Is being a Jew fundamentally about the observance of every detail of Jewish law (as Bekhorot implies), or does converting mean joining a covenantal community that sees itself as marginal, a community in which commandments are central, but perhaps not the defining characteristic (as in Yevamot)?
Daniel Gordis, “What, Not Who, Is a Jew?”, Sh’ma (March 2011), 12.