Many think the reason we use the hymnal is either because that's just how we've always done it, or because we're stodgy stubborn Lutherans. The assumption is usually made that the music is neutral and eventually we too will trade in our Hymns for the music we hear on Christian Radio. But Music is never neutral.
In our culture today music is used either as a form of entertainment or a tool to affect the mood. Retail stores will choose specific music to incite you to spend money. The radio plays a specific genre and style to tickle your ear. The elevator plays music which is suppose to keep you calm. But the music we hear in church is neither mood-setting nor entertainment driven.
Hymns sung in the context of the Divine Service are countercultural, preaching and teaching the Word of God, delivering the gifts of Christ, and resembling a short sermon set to music. Thus the value of hymnody is not found in its emotional effect upon the hearer or its appeal to the masses, but according to its objective substance, proclaiming the benefits of Christ under the cross.
It's not simply an argument for orthodox lyrics, like so many suggest. For we cannot set the words of "A Mighty Fortress" to a tune resembling something we might hear at an AC/DC concert or a Jazz club and expect it to be just as beneficial to those preparing to receive the Eucharist.
When orthodox lyrics are accompanied by a primary desire to provide entertaining sounds, the truth within the lyrics can easily be obscured and confused. The sacred claims of the text are easily overpowered by its blending with strong secular overtones, thus taking the timeless truths of scripture and making them subject to the capricious wind of the culture. This is not to argue traditional verse contemporary, organ verse guitar, nor any one genre over another, but simply to maintain the countercultural aspect of the liturgy which is intended to transform the culture through the Gospel, not bow to it.
The foundational purpose of hymnody is not to provide a performance which drives the congregation to clap and sway or have their livers quiver for Christ, but to feed the people with the sustaining Word of God, which gives life and salvation regardless of how well one "feels" they have encountered God in the experience.
Since the purpose of worship is for sinners to receive the gifts of Christ in Word and Sacrament, then success in worship is not dependent upon pew morale, driven by a mood-setting rhythm or a hip tune, but upon the Word of God, proclaimed and delivered in Christ. If we begin to suggest otherwise, that the Word of God is better delivered with a culturally "relevant" upbeat tempo, not only do we degrade God's Word in order to chase the skirt tails of Lady Relevance, but we lose the Gospel all together. For then it is not Jesus' blood-bought grace that we seek, but just another way to scratch the scabs of our itching ears.