I borrowed a book of St. Francis de Sales, sermons for Lent, and what little I've read I find a tad boring. I think it would be different if we could hear them delivered. It even says that in the Preface, something about how they only give a faint idea, in print, of the effect they had when they were delivered.
When I think of a born WRITER, as opposed to a speaker -- not that they weren't good at that as well -- I think of St. Teresa or St. Augustine.
They had a personal touch that kept most of their stuff from being too dry.
To be honest, I find a lot of spiritual writing boring. The spiritual life is something I prefer to experience rather than read about. Of course, to experience it, you have to know a little bit about it, and for that you have to read about it or at least listen to sermons.
What happens with spiritual writing, for me, is that I'll be going along thinking "Yeah yeah, I know that," and then a certain thought will leap out at me. Then I will grab onto that one thought and sort of masticate it for a while, I'll let it circle around my brain. This thought then becomes incorporated into my own prayers, my own way of seeing the world.
I guess, if I had to pick one saint to read, it would be St. Augustine since you could spend your life reading his works. I haven't even scratched the surface. You have the personal works like Confessions, the brainy works like City of God, and then the various polemics. He has the most variety in his writings by far, I'd say.
But then, of course, there is St. Thomas. The Summa is not something I'd want to read every day, and it is the farthest thing from personal, but it is intellectually stimulating beyond compare, and his other writings, like about the Gospel of St. John, for instance, are amazingly detailed. I just think his writing may be too heavy if it was ALL I had, I'd crave a writing style that was more "human."