When it comes to music books, my wife is no minimalist. We can pull out any number of theory books. So I've had a few to choose from, but these have helped me the most . . .
Chords in hymns are mostly major or minor triads with some inversions to make the parts easier to sing. As a pianist, knowing and playing simple triads is not enough. To play rich, interesting chords consider altered chords. In the example below we move from a I chord to a triad with an added sixth interval. This would be a C6 or I6 (not to be confused with a first inversion). It is a C6 because we play the C triad (C,E,G or I, iii, V) and add the vi of the scale. But the chord is all scrunched up.