In Colossians 3:16 (& Eph. 5:19), the benefit and purpose of singing is seen in three directions:
1. For others, "teaching and admonishing one another"
2. For one's self, "in your heart"
3. To God, "to the Lord"
"Let the word of Christ dwell in you richly in all wisdom; teaching and admonishing one another in psalms and hymns and spiritual songs, singing with grace in your hearts to the Lord."