When Colossians 1:28 and 3:16 are compared, it is quite clear that (at the minimum) some of our songs sung in church should have an admonishing/teaching function, and that the role of the pastor and head musician, in Paul’s view, would likely be similar. Examine the evidence yourself, and see chapter 2 of The New Worship PowerPoints category (listed here) for more detailed argument.
Sevenths with raised or lower fifths function mainly as harmonic intensifiers. Think of them grammatically as adjectives or adverbs. The dominant seven with a raised fifth has an augmented sound embedded within it, whereas the lowered fifth has a diminished sound.
Major ninth chords with no third occur with regularity in contemporary worship choruses. They are bright sounding. Like the rock alternating harmonies, they are helpful in projecting a degree of tension—even power. You probably won’t find them in any hymnal though.