I’m finishing up a seminary class on Paul’s epistles, and came across this really helpful quote from a commentary on Colossians by R.C. Lucas. When he comes to the passage familiar to many worship leaders, from Colossians 3:16, (“Let the word of Christ dwell in you richly, teaching and admonishing one another in all wisdom, singing psalms and hymns and spiritual songs, with thankfulness in your hearts to God”), he explains:
What is at issue here is the content of the young church’s hymns. The history of Christian awakening shows that whenever the word of Christ is recovered, it is received with great joy, a joy that can fully express itself only with songs of praise. What the apostle is concerned to see is that these songs are consistent with the word of Christ, or as we are bound to say nowadays, scriptural. A fair test of this is to be found by whether or not they echo a heartfelt spirit of thankfulness: genuine Christian praise is not primarily a vehicle for the expression of spiritual aspirations and experiences, so much as a celebration of God’s mighty acts in Christ… A gospel of grace must be echoed by songs of gratitude for grace.
Our job as worship leaders is not only to serve as guards of the content of the songs our churches sing; but as cultivators of the spirit with which they’re sung. It’s not enough for the content to be solid, although that’s important. We must help our congregations experience and express thankfulness and gratitude for grace. I heard Louie Giglio say in a sermon from his church that “extravagant grace leads to extravagant worship”. Paul would agree!
Worthily Magnify 
Very true – this verse calls us to allow our sung congregational praise to flow out of response to the objective truths of the gospel (e.g. Colossians 1-2, Ephesians 1-3). Good reminder to leaders to be making sure our congregation’s attitudes and motivation towards singing are right (as far as we’re able). By pointing them to Christ and all He is and has done in Calvary through the eternal word of God, we’re faithfully letting songs of praise and gratitude come authentically from their hearts. The content of the songs is critical as you say, because they are teaching people – but the motivation for singing or ‘spirit’ is so important too, which often people forget. Thanks for the reminder!!