I have always been influenced by writers who can efficiently clarify large, heady concepts with as few words as possible. Walter Brueggemann does just that in his often overlooked gem of a book, Spirituality Of The Psalms. It weighs in at a mere 96 pages and in it Brueggemann is as profound as he is brief in dealing with the subject of pain and suffering.
One other short, but mighty read is a book by C. Baxter Krueger. The Great Dance has completely transformed the way I view the Trinity.