Once a name for sinners who repented, this term now describes those who return to Orthodoxy.
Reprinted from The Jewish Religion: A Companion, published by Oxford University Press.
Baal Teshuvah means a repentant sinner, or literally "one who returns" from his evil ways. That a sinner is to be encouraged to return to God and repent of his sins is stressed by the Talmudic rabbis, following the biblical teachings about sin and repentance. According to one opinion in the Talmud, the repentant sinner is greater than one who has never committed any grievous sin.
There are two kinds of penitents: the sinner who repents out of fear and the sinner who repents out of love for God. Once the former has repented his sins are considered as if he had committed them unintentionally, but when a sinner repents out of love his very sins are counted as if they had been virtues. The Rabbis teach that it is a serious offence to taunt a penitent with his former evil deeds.
For the Saints of Germany sin and repentance are seen as stages in the spiritual life. Even the saints, for these medieval teachers, can only advance in spirituality by repenting of minor sins which for lesser mortals would be mere peccadilloes, the baal teshuvah thus becoming one highly advanced in the spiritual way. In times when conversions to other religions were not unknown among Jews, the name baal teshuvah was given especially to a convert to Christianity or Islam who had returned to the Jewish fold.
In the second half of the 20th century, there has emerged a strong baal teshuvah movement in which the name is given to those, especially young persons, formerly estranged from or ignorant of full Jewish observance, who have now returned to the fully Orthodox way of life. The name baal teshuvah has here lost its original meaning, which bordered on the pejorative, to denote something of a status symbol.
There are nowadays special yeshivot for the training of such returners, in which they are introduced gradually to all the niceties of Jewish rituals and observances. It is not uncommon for people belonging to this movement, once they have seen the light, to become intolerant zealots with the result that they are sometimes viewed with suspicion and hostility by their parents and former teachers, who are appalled at their fundamentalism.
However, the teachers at these institutions do try hard to promote tolerant attitudes on the part of their pupils, urging them not to look down on those who do not have their advantages. In contemporary American slang, the baal teshuvah is called, after the initial letters, a BT, in contradistinction to the FFB, "frum ['pious'] from birth." BTs now wear their name with pride, feeling superior to the FFBs; the latter react, as might have been expected, with derision.