The Babylonian Captivity of the Church

Prelude on the Babylonian Captivity of the Church  (October 1520) was the second of the three major treatises published by  Martin Luther  in 1520, coming after the  Address to the Christian Nobility of the German Nation  (August 1520) and before  On the Freedom of a Christian  (November 1520). It was a theological  treatise, and as such was published in  Latin  as well as German, the language in which the treatises were written.

In this work Luther examines the  seven sacraments  of the  Catholic Church  in the light of his interpretation of the  Bible. With regard to the  Eucharist, he advocates restoring the cup to the  laity, dismisses the Catholic doctrine of  Transubstantiation  but affirms the  real presence  of the body and blood of Christ in the Eucharist, and rejects the teaching that the  Mass  is a sacrifice offered to God.

With regard to  baptism, he writes that it brings  justification  only if conjoined with saving faith in the recipient; however, it remains the foundation of  salvation  even for those who might later fall and be reclaimed.

As for  penance, its essence consists in the words of promise (absolution) received by faith. Only these three can be regarded as sacraments because of their  divine  institution and the divine promises of salvation connected with them; but strictly speaking, only Baptism and the Eucharist are sacraments, since only they have "divinely instituted visible sign[s]": water in Baptism and bread and wine in the Eucharist. Luther claimed that  Confirmation,   Matrimony,   Holy Orders, and  Extreme Unction  are not sacraments.

The titular "captivity" is firstly the withholding the cup in the Lord's Supper from the laity, the second the doctrine of  transubstantiation, and the third, the Roman Catholic Church's teaching that the Mass  was  a sacrifice and a good work.  

The work is angry in tone, attacking the papacy. Although Luther had made a link tentatively in the address  To the Christian Nobility of the German Nation, this was the first time he forthrightly accused the  pope  of being the  Antichrist. It certainly heralded a radicalization of Luther's views-only a year before he had defended the validity of the sacraments, yet was now attacking them fiercely.

Although published in Latin, a translation of this work was quickly published in German by Luther's opponent, the Strasbourg  Franciscan  Thomas Murner. He hoped that by making people aware of the radical nature of Luther's beliefs, they would realise their foolishness in supporting him. In fact, the opposite proved true, and Murner's translation helped to spread Luther's views across Germany. The virulence of Luther's language however, was off-putting to some. After the publication of this work, with its harsh condemnation of the papacy, the renowned humanist  Erasmus, who had previously been cautiously supportive of Luther's activities, became convinced that he should not support Luther's calls for reform.