Adiaphora are not to deny Christian freedom, replace true worship, or interfere with the preservation of the pure doctrine...

The article about Christian freedom is at stake here. The Holy Spirit, through the holy apostle’s mouth, sincerely told His Church to preserve this article, as we have just heard. As soon as Christian freedom is weakened and human traditions are forced on the Church with coercion, as though it were wrong and a sin to omit them, the way is already prepared for idolatry. In this way, human traditions are multiplied and regarded as a divine worship, not only equal to God’s ordinances, but even placed above them.

Furthermore, idolaters are confirmed in their idolatry by such yielding and conforming in outward things, where there has not previously been Christian unity in doctrine. On the other hand, true believers are grieved, offended, and weakened in their faith. Every Christian, for the sake of his soul’s welfare and salvation, is bound to avoid both of these, as it is written:

Woe to the world for temptations to sin! (Matthew 18:7)

But whoever causes one of these little ones who believe in Me to sin, it would be better for him to have a great millstone fastened around his neck and to be drowned in the depth of the sea. (Matthew 18:6)

But what Christ says is to be especially remembered:

So everyone who acknowledges Me before men, I also will acknowledge before My Father who is in heaven. (Matthew 10:32)

However, this has always and everywhere been the faith and confession about such matters, by the chief teachers of the Augsburg Confession. We are following in their footsteps and we intend to persevere in their confession by God’s grace.

~BOC, FSD, X, 15-18