a•cous•tic (/əˈko͞ostik/) adj.: Relating to sound or the sense of hearing.
the•ol•o•gy (THēˈäləjē/) n.: God words.
Music is meant to be heard. In fact, you might say that if it's not heard, it's not actually music. You can own heaps of sheet music; little solid and hollow dots occupying some lines on a dog-eared, coffee-stained page. But until it actually enters time and space through the pulsing strings of a violin or the vocal chords of a soprano, it isn't music and can't be fully enjoyed. If the notes on the page aren't given voice and ushered into the airwaves by an instrument, then they are useless; they are not doing what they were given to do.
The apostle Paul speaks about the acoustic nature of the Christian faith in Romans 10:13-17:
For “everyone who calls on the name of the Lord will be saved.” How then will they call on him in whom they have not believed? And how are they to believe in him of whom they have never heard? And how are they to hear without someone preaching? And how are they to preach unless they are sent? As it is written, “How beautiful are the feet of those who preach the good news!” But they have not all obeyed the gospel. For Isaiah says, “Lord, who has believed what he has heard from us?” So faith comes from hearing, and hearing through the word of Christ. (ESV)
When I teach these verses, I like to sum it up as follows: "The word of the Gospel: if it ain't spoken, it ain't heard, and it don't work." (For whatever reason, terrible grammar makes these kinds of things stick.) Faith—that external gift, unmerited by works, by which we are objectively declared "righteous" in God's sight (Romans 4)--that faith comes by hearing the word of Christ. So if that word is not spoken, how can it be heard, and therefore, how can it do its work? If it is not ushered into the airwaves by someone speaking it, how can it do its work of giving faith?
Answer: it can't. If it ain't spoken, it ain't heard, and it don't work.
Martin Luther puts it far more eloquently in his Large Catechism: "...for where Christ is not preached, there is no Holy Ghost who creates, calls, and gathers the Christian Church, without which no one can come to Christ the Lord" (LC, Part 2, Article III, 45).
Jesus himself highlighted this acoustic reality in Luke 24:
Then he said to them, “These are my words that I spoke to you while I was still with you, that everything written about me in the Law of Moses and the Prophets and the Psalms must be fulfilled.” Then he opened their minds to understand the Scriptures, and said to them, “Thus it is written, that the Christ should suffer and on the third day rise from the dead, and that repentance and forgiveness of sins should be proclaimed in his name to all nations, beginning from Jerusalem. You are witnesses of these things. And behold, I am sending the promise of my Father upon you. But stay in the city until you are clothed with power from on high.” (Luke 24:44-49, ESV)
This actually gives the Church clarity concerning what she ought to be about: proclaiming into eardrums the very word through which the Holy Spirit works and which God has promised will not return to him empty. We are all acoustic theologians. That Gospel is, after all, a message that only Christ's bride possesses to proclaim. Therefore all that we do and say is subsumed under the banner of Christ's cross and his empty grave proclaimed, and that for the forgiveness of sinners. So, the Gospel is not buying homeless people food. It's not serving soup at a warming center. It's not building houses for the less fortunate. It's not rescuing stray dogs and cats. It's not living an environmentally aware lifestyle as a steward of the earth. It's not making sure people live moral and upright lives by being a 'good example'. It's not funding cures for cancer or lobbying for this or that legislation. While all of these things are good and worthwhile, they are not the Gospel. We do not "preach the Gospel always and when necessary use words" (St. Francis of Assisi). This is impossible. Why?
Because the Gospel is precisely acoustic God-words.
Words about Christ who was crucified for our sins and raised for our justification (1 Corinthians 15:3-4). Words spoken physically into time and space. Words that vibrate airwaves and bounce off of sinners' eardrums. Words that till the crusty soil of our hearts. Words that proclaim repentance and the forgiveness of sins (Luke 24:47). And if those words ain't spoken, they ain't heard, and they don't work. But when they are spoken, take heart. For it is through those acoustic words, spoken from sinners' lips, that God miraculously delivers his saving goods.
Incredible, that God would join his word to the mundane stuff of his creation; not only to sound waves that echo off of our eardrums, but also to water that washes over our skin and to bread and wine that place into our mouths the very body and blood of Christ. Yes, God uses that powerful, Word-laced, promise-laden stuff to deliver his external, objective goods of salvation and forgiveness.
Yes, even to sinners like us.