Fr. Stephen Brock examines the metaphysics of petitionary prayer through the perspectives of C.S. Lewis, Peter Geach, and especially Thomas Aquinas, highlighting how Aquinas’ account uniquely reconciles divine immutability, providence, and the real efficacy of prayer.This lecture was given on February 7th, 2025, at Duke University.For more information on upcoming events, visit us at thomisticinstitute.org/upcoming-events.About the Speaker:Stephen L. Brock is a priest of the Prelature of Opus Dei (ordained 1992). He is Ordinary Professor of Medieval Philosophy at the Pontifical University of the Holy Cross in Rome, where he began teaching in 1990.  Since 2008 he has been an Ordinary Member of the Pontifical Academy of St. Thomas Aquinas.  Since 2017 he has been a visiting professor in the Department of Philosophy of the University of Chicago. He is the author of Action & Conduct: Thomas Aquinas and the Theory of Action (T&T Clark, 1998); The Philosophy of Saint Thomas Aquinas: A Sketch (Wipf & Stock, 2015); The Light that Binds: a Study in Thomas Aquinas's Metaphysics of Natural Law (Wipf & Stock, 2020); and numerous articles on various aspects of Aquinas’s thought.This project/publication was made possible through the support of Grant 63391 from the John Templeton Foundation. The opinions expressed in this publication are those of the author(s) and do not necessarily reflect the views of the John Templeton Foundation.Keywords: Aquinas, C. S. Lewis, Divine Immutability, Metaphysics of Prayer, Petitionary Prayer, Peter Geach, Providence, Thomistic Philosophy, Time and Eternity, Work and Prayer