One of my favorite quotes: "The man who, knowing the right, fails to do it, loses the power to know what is right; and the man who, having the power to do right, is unwilling, loses the power to do what he wills." St. Augustine, De Libero Arbitrio
Also, Lila Rajiva posted a fine quote from Lord Acton: "Liberty is not the power of doing what we like, but the right of being able to do what we ought."
Lila posted an essay of mine on Owen Barfield's Saving the Appearances -- read at http://mindbodypolitic.com/?p=562
The essay on Barfield is one I have worked on and revised over several years. I have always felt it was important to get a grasp of the ideas of this challenging thinker and that really knowing what he says would make a difference to one's life, deeply, inwardly. Every time I work on the piece it gets a little better.