This site has a view of Regulative Principle, which is not the view of many Reformed either, so its condemnations is not just at today's Lutherans but also at fellow Reformed as well.
The site reads:
http://www.truecovenanter.com/truelutheran/truwrshp.htm"It is well known that most Lutherans have always retained as part of their service to God both the Lord's day instituted by Christ as well as most of the major "holy days" instituted by the Papists. The practice is inconsistent with the principles laid down in the Formula of Concord which asserts, 'We believe, teach, and confess that in time of persecution, when a plain [and steadfast] confession is required of us, we should not yield to the enemies in regard to such adiaphora, as the apostle has written Gal. 5,1: Stand fast, therefore, in the liberty wherewith Christ hath made us free, and be not entangled again in the yoke of bondage. Also 2 Cor. 6,14: Be ye not unequally yoked together with unbelievers, etc. For what concord hath light with darkness? Also Gal. 2,5: To whom we gave place, no, not for an hour, that the truth of the Gospel might remain with you. For in such a case it is no longer a question concerning adiaphora, but concerning the truth of the Gospel, concerning [preserving] Christian liberty, and concerning sanctioning open idolatry, as also concerning the prevention of offense to the weak in the faith [how care should be taken lest idolatry be openly sanctioned and the weak in faith be offended]; in which we have nothing to concede, but should plainly confess and suffer on that account what God sends, and what He allows the enemies of His Word to inflict upon us.'
"Here, in the Epitome's fourth affirmation in chapter 10, we have a clear affirmation that when the enemy of the Gospel has commanded an observation as moral duty, sinful to neglect, the Christian should STAND FAST in the liberty wherewith Christ has made him free, by defending his Christian Liberty through an open dissent from that practice or profession imposed by the enemies of the Gospel. Certain it is that the entire liturgical year, with Christ-Mass, Ishtar, Good-friday, &c. is all one big idolatrous chain of bondage imposed by no authority but that of Antichrist."
Here we see the article actually claiming the Lutheran Book of Concord denouncing celebrations of Christmas, Easter, etc., as practices of the antichrist. It takes a statement about Christian liberty and turned it into what the Book of Concord does NOT say- and that is that Christians are not at liberty to celebrate such days. Yes, the site does say Christians are to defend their liberty by OPEN DISSENT against these practices. But to the Book of Concord, that is precisely antithesis to Christian liberty. The Book of Concord was stating that Christians are at liberty to not celebrate these days even when those in authority demand they practice those days. It does not say celebrating them means submitting to the authority of the antichrist.
Here are other statements that show the Book of Concord (cited particularly from Epitome):
http://www.bookofconcord.org/fc-ep.html#X.%20Church%20Rites"4] 2. We believe, teach, and confess that the congregation of God of every place and every time has the power, according to its circumstances, to change such ceremonies in such manner as may be most useful and edifying to the congregation of God. "
Here is the statement in that same context that shows indeed that congregations can practice these ceremonies as long as they are useful and edifying. More we also see the Book of Concord states:
"7] 5. We believe, teach, and confess also that no Church should condemn another because one has less or more external ceremonies not commanded by God than the other, if otherwise there is agreement among them in doctrine and all its articles, as also in the right use of the holy Sacraments, according to the well-known saying: Dissonantia ieiunii non dissolvit consonantiam fidei, Disagreement in fasting does not destroy agreement in faith. "
These is the very statement that came after what the Reformed article cited from the Book of Concord in claiming Lutherans today are not following the Book of Concord since they celebrate holidays like Christmas. Yet, here, the Reformed article is doing the very thing the Book of Concord said NOT to do- that is to condemn another church for having external ceremonies not commanded by God. I would suggest it is the Reformed article that is not keeping with the principle of the Book of Concord.
As pointed out, what is cited by the Reformed article is a statement about Christians are at liberty to celebrate or not celebrate the holidays in question. If it becomes a matter of these holidays being turned as required commandment/law or twisted to become the gospel in itself, Lutherans are to oppose being forced to celebrate them. But they are not to condemn others who do celebrate them as long as it is done out of principle of Christian liberty. That is in following with what the Augsburg Confession not only said about Christmas and Easter, but also Sunday which ironically the Reformed themselves, regardless of whether they follow the regulative principle or not, keep.
