In Luther's opinion the elementary doctrines which form the subject-
matter of the Catechism are comprised in the three traditional parts:
Decalog, Creed, and Lord's Prayer. These he considered to be the gist of
the doctrine every one must learn if he would be regarded and treated as
a Christian. "Those who are unwilling to learn it," says Luther, "should
be told that they deny Christ and are no Christians; neither should they
be admitted to the Sacraments, accepted as sponsors at Baptism, nor
exercise any part of Christian liberty." (CONC. TRIGL. 535, 11.) Of
course, Luther considered these three parts only a minimum, which,
however, Christians who partake of the Lord's Supper should strive to
exceed, but still sufficient for children and plain people. (575, 5.)
Even in his later years, Luther speaks of the first three parts as the
Catechism proper.
However, probably in consequence of the controversy with the
Enthusiasts, which began in 1524, Luther soon added as supplements the
parts treating of Baptism, the Lord's Supper, and Confession. In the
Large Catechism, where Baptism and the Lord's Supper appear as
appendices, Luther emphasizes the fact that the first three parts form
the kernel of the Catechism, but that instruction in Baptism and the
Lord's Supper must also be imparted. "These" (first three), says he,
"are the most necessary parts, which one should first learn to repeat
word for word. ... Now, when these three parts are apprehended, it
behooves a person also to know what to say concerning our Sacraments,
which Christ Himself instituted, Baptism and the holy body and blood of
Christ, namely, the text which Matthew and Mark record at the close of
their gospels, when Christ said farewell to His disciples and sent them
forth." (579, 20.) Luther regarded a correct knowledge of Baptism and
the Lord's Supper not only as useful, but as necessary. Beginning his
explanation of the Fourth Chief Part, he remarks: "We have now finished
the three chief parts of the common Christian doctrine. Besides these we
have yet to speak of our two Sacraments instituted by Christ, of which
also every Christian ought to have at least an ordinary, brief
instruction, because without them there can be no Christian; although,
alas! hitherto no instruction concerning them has been given." (733, 1.)
Thus Luther materially enlarged the Catechism. True, several prayer- and
confession-books, which appeared in the late Middle Ages, also treat of
the Sacraments. As for the people, however, it was considered sufficient
for laymen to be able to recite the names of the seven Roman sacraments.
Hence Luther, in the passage cited from the Large Catechism, declares
that in Popery practically nothing of Baptism and the Lord's Supper was
taught, certainly nothing worth while or wholesome.