As regards the difference between the Lutheran and the Reformed Church, my friends, the Lutheran people, at least in former times, imagined that the whole difference was this, that in reciting the Lord's Prayer in German, the Lutheran put the word "Father" first, the Reformed the word "Our" and that in the Lord's Supper, wafers, which are not broken, are used in the Lutheran Church, while the Reformed churches use ordinary bread, which they break at the distribution or before. For this horrible ignorance the unfaithful ministers of our Church are to be blamed. They have shamefully neglected their people.
In view of this ignorance it is, of course, not surprising that these poor Lutherans finally yielded to overtures for a union with the Reformed. Recently, however, a change has taken place: the violently enforced establishment of the United Church in the very country where it was attempted first, in Prussia, has brought about a reconsideration by our beloved Lutheran people of the points of difference between the Reformed and the Lutheran Church. In 1817, when the Union was inaugurated, Claus Harms, pastor and professor at the University of Kiel, published a new series of Ninety-five Theses for use at the celebration of the Tercentenary of the Reformation. In Thesis 95 he says: "A copulation is now contemplated, which is to enrich that poor handmaiden, the Lutheran Church." However, he adds this warning: "Do not attempt it on Luther's grave; his bones will take on new life, and then the Lord have mercy on you!" His prophecy has been fulfilled. Nowadays any Lutheran child that has received at least a passable instruction in the Christian doctrine knows that there is indeed a great difference, involving the principal articles of Christian doctrine, between the Lutheran and the Reformed Church. To-day the Lutheran people are well informed on this point: Lutherans adhere firmly to the words of Christ, forever true: "This is My body; this is My blood." Lutherans, accordingly, believe that the body and blood of Christ are substantially and truly present in the Holy Supper and are administered to, and received by, the communicants, while those clear words, plain as daylight, are interpreted by the Reformed to mean: "This signifies the body of Christ; this signifies His blood." Accordingly, the Reformed contend that the body and blood of Christ are removed from the Holy Supper as far as the heavens are from the earth, because they are limited to the heavenly mansions and His return to earth is not to be expected until the Last Day.
Nowadays all Lutheran people know that according to Scripture, the Book of eternal truth, Holy Baptism is the washing of regeneration, a means by which regeneration is effected from on high through the Holy Spirit; while the Reformed contend that Baptism is merely a sign, symbol, or representation of something that has previously taken place in a person.
Nowadays all Lutheran people know that the human nature of Christ, through its union with the divine nature, has received also divine attributes, namely, that omniscience, omnipotence, omnipresence, and the honor of adoration have been communicated to it; while the Reformed contend that between the man Christ and other men there is a difference only of degree, namely, that Christ has received greater gifts. However, even the highest gifts which His human nature possesses are claimed to be creature gifts, the same as in other creatures.
Nowadays all Lutheran people know that according to the Holy Scriptures the saving grace of the Father is universal; so is the redemption of the Son, and likewise the effective calling of the Holy Spirit through the Word; while the teaching of the Reformed Church on these three points is particularistic, because the Reformed most emphatically contend that God has created the greater part of the human race unto eternal damnation and has accordingly assigned them even in eternity to everlasting death. In the clear light of the precious, saving Gospel this is an appalling, a horrible doctrine.
To be brief, every Lutheran knows nowadays that the difference between the Lutheran and the Reformed Church is fundamental: it lies, not on the circumference, but in the very center of the Christian doctrine.
from C.F.W. Walther, "Law and Gospel, Fourteenth Evening Lecture" (January 16, 1885).