The Missing Piece

Unlike most beginning meditation practices, which provide a simple object of focus for the attention (like following the breath or reciting a mantra), Centering Prayer provides no such focal point; it merely teaches the practitioner how to release the attention promptly when it gets tangled up in a thought. Echoing the teaching of The Cloud of Unknowing (which turned out to be Centering Prayer's principal source), a "thought" is defined as anything that brings attention to a focal point-- "as the eye of an archer is upon the target he is shooting at," the anonymous medieval author illustrates. His instruction is to immediately release the object of attention and return to the "cloud of unknowing," his metaphor for a more diffuse, objectless awareness which he sees as the foundational prerequisite for what he calls "the work of contemplation." 

Cynthia Bourgealt shares more in this essay.