262. The Nineteenth Bracha
Tefillah u’Birkas Kohanim 1:10
Voluntary prayers are never recited by the congregation because freewill offerings were not communal. Even an individual should not recite musaf twice, intending one to fulfill his obligation and the other as a voluntary prayer; this is because the musaf sacrifice was never brought as a freewill offering. One of the Geonim ruled that it is prohibited to recite voluntary prayers on Shabbos or yom tov since freewill offerings were not brought on those days.
Tefillah u’Birkas Kohanim 2:1
In the days of Rabban Gamliel, there was an increase in the number of heretics among the Jews. These heretics were luring the Jews away from the service of God. Because of this compelling need, Rabban Gamliel and his court composed a bracha asking God to eradicate the heretics. They inserted this bracha into Shemoneh Esrei so that everyone would become familiar with it. Accordingly, there are nineteen brachos in Shemoneh Esrei (even though “Shemoneh Esrei” means “eighteen”).