I have been reading Cynthia Bourgeault's The Heart of Centering Prayer: Nondual Christianity in Theory and Practice.  It is a book to read slowly and take time for reflection on what I have read. Since I am still in the second part, I can only say that I find the book helpful.  My Lenten reading is really on John's Gospel. I can only read a few minutes of The Good Wine, by Bruno Barnhart each day as he gives me too much to think about.