Here in a nutshell is the entire glorious mystery of the New Testament. By virtue of his resurrection, Jesus is alive in such a way that he can be both “with us” and “for us.” Simultaneously he is “in the midst of the assembly” and in the heavenly Jerusalem ever interceding for us. A permanent Singer has been installed. From one perspective, he sings with us in the church; from another he intercedes for us in heaven. When the church gathers in worship, earth and heaven converge. When we sing we are not singing by ourselves. There is a higher song going on above ours and a deeper song going on beneath ours.
Reggie Kidd, With One Voice: Discovering Christ's Song in Our Worship (Grand Rapids: Baker Books, 2005) p. 115.
The author also has a website with lots of helpful resources on worship, biblical studies, music, and a blog.