“The Sign of the Cross: The Fifteen Most Powerful Words in the English Language” by St. Francis de Sales; Sophia Institute Press.
“The Sign of the Cross in the Nineteenth Century” by Mgr. Jean-Joseph Gaume; Loreto Publications.
“Fire from Above: Christian Contemplation and Mystical Wisdom” by Dr. Anthony L. Lilles; Sophia Institute Press.
“Hidden Mountain, Secret Garden: A Theological Contemplation on Prayer” by Anthony Lilles; Discerning Hearts.
Catechism of the Catholic Church: CCC #1131, CCC #1670