With my tongue partly in my cheek I must ask and comment concerning your definition of liturgy. Why must man make an order so that God can serve him with the His Word and His Sacraments?
It certainly seems to me as though the Scriptures and our Lutheran Confessions in multiple places teach that at least some of the order (or ritual or form) that we use for worship is instituted and ordained by God, if not explicitly by spoken word and command then implicitly by action and practice.
First, the office of the ministry for the preaching of the Word and the administration of the sacraments is divinely instituted. “To obtain such faith [as described in AC IV] God instituted the office of the ministry, that is, provided the Gospel and the sacraments.” (AC V.31, Tappert) This is not a “man-made” order for the delivery of God’s gifts.
Also, prayer to God in Jesus Name (John 15:7); the Lord’s Prayer; exercise of the office of the keys – forgiveness of sins; confession of faith (Matt 10:32); enactment of baptism; fellowship (common offering); and celebration of the Lord’s Supper; these aren’t “man-made” things either but are certainly part of our order of worship.
Should we be doing things in worship that aren’t instituted by God’s Word? “…God is pleased only with services instituted by His Word and done in faith.” (AP XXVIII.70, Tappert) This seems to speak against any “man-made” order.
Acts 2:42 – “And they devoted themselves to the apostles’ teaching and fellowship, to the breaking of the bread, and to the prayers.” This suggests a four fold structure and order of Word and Sacrament worship in the early church that they held in common and that was pleasing to God who added to their number daily.
1 Corinthians 14:40 – “All things should be done decently and in order” – Kata taxin is not just an orderly way, but a given order; it has a military history concerning the arrangement or order of soldiers for battle, and in LXX is used to describe the station of the priests at the temple.
We certainly do not create a law to burden consciences or become legalists about this lest we cease to be Lutheran; neither do we so quickly walk away from what we as a Synod have agreed to walk together on and jettison without considering our neighbors what has been handed down to us and is founded on the Word of God and the practice of the apostles, even if people don’t know why we do it. The problem of “we’ve always done it that way” is a problem of poor pastoral teaching on the subject, not a problem with the order.
I think there is much more that can be said, about what is commanded in Scripture, what is forbidden in Scripture, and then what is neither commanded nor forbidden (adiaphora) by Scripture; as well as when adiaphora ceases to be adiaphora. More can be said about Jesus’ practice and the structure He uses in Luke 24 with the Emmaus disciples, but attempting to also follow your second self imposed rule, I will stop so that perhaps what I have already written will be read.
I must disclose that while I learned much of this at the seminary, what I have written above is a summary of what came to me courtesy of a presentation in Ainsworth, NE by Dr. Kleinig this past fall. I know this presentation is available on DVD at the Lutheran Catechetical Society.