Intrepid Lutherans has Dr C.F.W. Walther's response to a question about using Methodist hymns in a Lutheran Sunday School in their article, "C.F.W. Walther: Filching from sectarian worship resources equals 'soul murder'". This was part of Dr Mark DeGarmeaux's presentation, "Sacramental Worship, Sacramental Preaching: Treasures of our Lutheran Church." (pdf, 10 pgs, 280 KB)
Here is that letter:
This morning I received your worthy letter, written on the 19th of the month. In your letter you ask for my opinion on whether it is advisable to introduce the singing of Methodist songs in a Lutheran Sunday School. May what follows serve as a helpful reply to your questions:
No, this is not advisable, rather very incorrect and pernicious.
Our church is so rich in hymns that you could justifiably state that if one were to introduce Methodist hymns in a Lutheran school this would be like carrying coals to Newcastle. The singing of such hymns would make the rich Lutheran Church into a beggar which is forced to beg from a miserable sect. Thirty or forty years ago a Lutheran preacher might well have been forgiven this. For at that time the Lutheran Church in our country was as poor as a beggar when it comes to song books for Lutheran children. A preacher scarcely knew where he might obtain such little hymn books. Now, however, since our church itself has everything it needs, it is unpardonable when a preacher of our church causes little ones to suffer the shame of eating a foreign bread.
A preacher of our church also has the holy duty to give souls entrusted to his care pure spiritual food, indeed, the very best which he can possibly obtain. In Methodist songs there is much which is false, and which contains spiritual poison for the soul. Therefore, it is soul-murder to set before children such poisonous food. If the preacher claims, that he allows only "correct" hymns to be sung, this does not excuse him. For, first of all, the true Lutheran spirit is found in none of them; second, our hymns are more powerful, more substantive, and more prosaic; third, those hymns which deal with the Holy Sacraments are completely in error; fourth, when these little sectarian hymnbooks come into the hands of our children, they openly read and sing false hymns.
A preacher who introduces Methodist hymns, let alone Methodist hymnals, raises the suspicion that he is no true Lutheran at heart, and that he believes one religion is as good as the other, and that he thus a unionistic-man, a mingler of religion and churches.
Through the introduction of Methodist hymn singing he also makes those children entrusted to his care of unionistic sentiment, and he himself leads them to leave the Lutheran Church and join the Methodists.
By the purchase of Methodist hymn books he subsidizes the false church and strengthens the Methodist fanatics in their horrible errors. For the Methodists will think, and quite correctly so, that if the Lutheran preachers did not regard our religion as good as, or indeed, even better than their own, they would not introduce Methodist hymn books in their Sunday schools, but rather would use Lutheran hymn books.
By introducing Methodist hymn books, the entire Lutheran congregation is given great offense, and the members of the same are lead to think that Methodists, the Albright people, and all such people have a better faith than we do.
This may be a sufficient answer regarding this dismal matter. May God keep you in the true and genuine Lutheran faith, and help you not to be misled from the same, either to the right or to the left.
Your unfamiliar, yet known friend, in the Lord Jesus Christ,
C. F. W. Walther
St. Louis, Missouri
January 23, 1883