In I Chronicles 6:31-32, the record is left there to you and me of the service of song ministering. This trained choir ministered to the congregation; they were performing duties of personal service in terms of music. To do this rightly in their circumstance, one has to be prepared. Music is every bit as effective at ministering to the congregation as the spoken word, but much more difficult because it requires time-consuming training to do it in the way that is being described here in Chronicles.