Here’s the link to article XV: https://bookofconcord.org/augsburg-confession/of-ecclesiastical-usages/
The term “ecclesiastical usages” refers to such traditions as:
- Daily hours of prayer
- The use of clerical vestments and churchly paraments
- The church calendar (i.e. seasons such as lent, easter, advent, etc.)
- The order of readings (i.e. the lectionary)
- Collects and other ancient prayers
- The burning of incense
- Processionals
The Lutheran confessors set forth a conservative principle of worship. If a tradition is conducive to tranquility and good order and can be observed without sin, then it should be retained.
This automatically rules out some customs. Article XXI points out that we cannot pray to the saints. Articles XXII and following deal with other abuses that had grown up in the church and needed correction.
However, many ancient traditions are useful. For example, the Daily Offices teach us to hear the scriptures and to pray. Vestments, processionals, and incense can add beauty to the divine service. When rightly understood, they can help worshippers to hear the Word. If traditions can be observed without sin, then the church should keep them.
At the same time, the article points out that such observances are not necessary to salvation. We are not required to observe the canonical hours, or follow the lectionary, or to burn incense. Congregations have freedom in this matter. If a custom has become burdensome or it no longer has meaning, then it may be discarded.
The third paragraph points out the danger inherent in observing traditions. Let’s consider the example of Lent. Many Christians fast from meat (or something else) during the forty days leading up to Easter. This can be a meaningful discipline, and it may help us to pray. However, if we think that it makes us more pleasing to God, then it is harmful. We need to constantly be reminded that our traditions do not earn us anything. God won’t love you more if you fast. He won’t love you less if you don’t fast.
We can also apply this article to the use of contemporary music in the church. We are free to use guitars, drum kits, etc. We are free not to do so. However, we should be discerning about the songs we sing, and we should always keep Word and Sacrament at the centre of our worship.