“Father George Timko, a Greek Orthodox parish priest, says, “Christianity became trapped at some point by thinking that prayer is verbalization and asking.  That’s a wrong understanding of prayer.  The Greek word prosevkomai [translated as "prayer"]…simply means to be in a mindful state of awareness. Theoria [usually translated as "contemplation"] is watching, observing, simply looking.  It is an interior looking of the mind, of paying attention without expectations.”

From Chapter 6 of Sacred World: The Shambhala Way to Gentleness, Bravery, and Power by Jeremy & Karen Hayward

Thomas Keating is a well respected contemplative prayer teacher and author. He founded the centering prayer movement. His books can be found here: selection of books by Thomas Keating.