This little 12th-century Cistercian treatise is one of the best-ever works on contemplation from a Christian source. Record of its authorship was dimmed for centuries, and it found itself erroneously attributed to Bernard of Clairvaux, Guigo the Carthusian, and Bonaventure.

Never officially impeached on any count, this document was instead consistently praised for the practical use of a spiritual elite. Yet it sometimes strikes notes surprisingly reminiscent of Valentinian gnosis, such as the division of men into groups governed by their animal, rational, and spiritual principles.

"To refuse to be perfect is to be at fault. Therefore the will must always be fostered with this perfection in view and love made ready. The will must be prevented from dissipating itself on foreign objects, love preserved from defilement. For to this end alone were we created and do we live, to be like God; for we were created in his image." (II.XVI.259)

William counsels a moderated asceticism with respect to diet and sleep, but a surpassing discipline of individual activity to train the will, and a rejection of external images in favor of inward contemplation. And at the last, real spiritual attainment must be kept secret.