Article XV: Of Ecclesiastical Usages.
Of Usages in the Church they teach that those ought to be
observed which may be observed without sin, and which are
profitable unto tranquillity and good order in the Church, as
particular holy-days, festivals, and the like.
Nevertheless, concerning such things men are admonished that
consciences are not to be burdened, as though such observance
was necessary to salvation.
They are admonished also that human traditions instituted to
propitiate God, to merit grace, and to make satisfaction for
sins, are opposed to the Gospel and the doctrine of faith.
Wherefore vows and traditions concerning meats and days, etc.,
instituted to merit grace and to make satisfaction for sins,
are useless and contrary to the Gospel.
This is an interesting (and seemingly light and innocent) topic of the Augsburg Confession, but one heavy on the minds of most worshippers. Essentially, the Reformers are here talking about liturgical or pious actions performed during worship or at other times that are supposed to observed for the sake of "acting out" the faith. Feast days of the church year like Easter and Christmas are included here, plus feasts for the saints. I imagine also would be included things like fasting before worship on Sunday mornings, abstaining from fish on Friday, giving up some kind of food during Lent, etc.
The rule is also quite simple- if the usage draws people into sin and temptation, don't do it. What is temptation and sin? When the usage is confused with the work Christ alone does for us in propitiating God, meriting grace, or making satisfaction for sin. In other words, when the usage is perceived as a human work that accomplishes salvation apart from or above and beyond the work of Jesus Christ, it is a usage that should be gotten rid of. I imagine they also mean any usage that leads people to other kinds of sin.
Here's my current short list of usages that trouble me, some because I feel drawn to do them, others because I think they show something false I wish weren't shown through action:
1. The tri-fold crossing over forehead, lips and heart before reading the gospels. I believe this is a wonderful non-verbal response to the gospel on the part of the congregation and pastor. It should be re-instituted.
2. The lifting up of the offering basket in front of the altar or cross- get rid of it.
3. Genuflecting, and bowing during the words of institution- yes, use it.
4. Old versus new Lord's Prayer- this is one of the most common topics to come up in our congregation. Almost everyone believes the old should be used. I tend to agree.
That's enough of a list to get us started. I believe the point is that the usages are for the sake of good order in the church, and they are encouraged if they teach the Christian faith purely rather than teaching that our actions merit salvation. They are there for building up our faith by doing things that we believe let us freely show our love of God and honor His Word, not to get anything, but simply because we are called to worship in that way.