1529 · Martin Luther, The Large Catechism 5
Now, what is the Sacrament of the Altar? Answer: It is the true body and blood of our Lord Jesus Christ, in and under the bread and wine which we Christians are commanded by the Word of Christ to eat and to drink. And as we have said of Baptism that it is not simple water, so here also we say the Sacrament is bread and wine, but not mere bread and wine, such as are ordinarily served at the table, but bread and wine comprehended in, and connected with, the Word of God. It is the Word (I say) which makes and distinguishes this Sacrament, so that it is not mere bread and wine, but is, and is called, the body and blood of Christ.