"Psychiatrists," he writes, "aren’t known for believing in God or angels. But some do, and I guess I’m one of them." After reviewing the history of angels not only in the Jewish and Christian faiths but also in other religious and spiritual traditions throughout the world, he notes that the word "angel" is derived from the Greek word for messenger. Angels are personal go-betweens linking individual human beings with God. Flach sees seven cardinal virtues of angels: choosing, knowing, loving, communicating, guiding and protecting, healing and helping, and spiritually growing. Flach describes his book’s message as the idea of "human beings learning something from the qualities attributed to angels that they might find valuable in their own very real, very visible lives here on earth." With respect to the role of science in the study of angels, he notes, "Maybe we scientists can’t prove there are angels. But we can’t prove there aren’t either."