"Changes in the liturgy take on a momentous significance for the believer, for they are changes in his experience of God – changes, if you wish to be Feurbachian, in God himself..." (Fuerbach was a19th century student of Hegel, noted for his attack on orthodox Christianity, The Essence of Christianity, where he surmised "in the consciousness of the infinite, the conscious subject has for his object the infinity of his own nature.")
Do you ever read something you wish you would have written or said? Here we have a single sentence written by someone well known but whose words say exactly what needs to be said about the changes we make in the liturgy. Though the writer was not Luther, Luther understood this implicitly. That is why Luther was so hesitant to change what the people heard and saw in the liturgy. He knew that these were not merely outward changes but changes in the way we know God. By extension we might also say that these liturgical changes are also then a change in the God whom we know -- not by the change of His essence but by the change of our perception of that essence which the liturgy is there to convey.
The writer, lest any of you be shocked, is none other than Joseph Cardinal Ratzinger, writing the Preface to A. Reid’s The Organic Development of Liturgy (whom we now call Benedict XVI).
The reason that folks like me get so upset when the liturgy is radically altered or ditched in favor of something different, is not that we are purists or traditionalists (though some of us might be). The reason we are up in arms is that this represents a change to the faith and experience of God for the believer himself. When we change the liturgy where God is known to us in the Word and Sacraments and witnessed in the historic words that address Him in prayer and prayer, we change the faith, we change the experience of God, and ultimately, we change the God whom we perceive through the liturgy. That is not to say that God changes. He does not. But is it the same God who is worshiped in the Divine Service with its appointed propers and vibrant sacramental identity and the one who is worshiped by contemporary song (that speaks feeling instead of truth) and whose Word is used to elevate the present, pursue happiness, and obtain pleasure?
When we change what happens on Sunday morning, we change the faith, we change the way we experience God, and we, ultimately, change our very perception of who this God is... That is why we are so concerned!