Perhaps Martin Luther understood this better than anyone. During the Reformation, the most popular way doctrine spread was not through the intellectual discourses between the theological heavyweights, but through hymns! And specifically hymns in the language of the people.
Martin Luther recognized the power and effectiveness of these songs, and in fact, he went on to write many hymns to teach and edify the church, but he also knew the dangers that would threaten to enter the church through song. Which is why he wrote these words:
False masters now abound, who songs indite;
Beware of them, and learn to judge them right:
Where God builds up his Church and Word, hard by
Satan is found with murder and a lie.
False teachers don't always enter the church as Pastors or Sunday School teachers, but also as hymn/worship music writers, and music ministers. It is a sobering thought to be given the responsibility to discern what is right and wrong for a congregation to sing. To those who are in such a position I hope Luther's words of warning impact you in the way they have impacted me. My prayer for myself and for those in a similar position is that God would grant His grace that we may continually be able to "judge them right."
By the way, I love that picture of Luther because it reminds me of myself...sitting at the table with my instrument, a drink on the table, papers scattered, children playing in the room, dog on the floor...that table even looks like mine.