T.S. Eliot's "Four Quartets." I know that answer is probably out of fashion, but it's the only book I have that I wore out.
The music of it is the first of many reasons why—both on the micro and macro level. I mean the individual words, and the lineation and syntax, and the tonal movements in the sections. We used the ending lines in our wedding vows forty years ago, so I can say that I found inspiration on a personal level and as a poet.