Pray continually, Paul urged the Thessalonians. The early church fathers took this one step further: continually make the sign of the cross.
"In all our travels and movements, in all our coming in and going out, in putting on our shoes, at the bath, at the table, in lighting our candles, in lying down, in sitting down, whatever employment occupies us, we mark our foreheads with the sign of the cross," wrote Tertullian at the turn of the third century, A.D. In the fourth century, St. John Chrysostom (apparently anticipating an American Express slogan) wrote, "never leave home without making the sign of the cross."
How the sign of the cross—the motion of the hand over the torso, up, down, then side-to-side—made its way from the early church to us today is a lesson in church history, as you can see in two new books: The Sign of the Cross: The Gesture, the Mystery, the History, by Andreas Andreopoulos (Paraclete Press, 2006) and The Sign of the Cross: Recovering the Power of the Ancient Prayer, by Bert Ghezzi (Loyola Press, 2006). (The sign of the cross as a benediction, made outwardly rather than towards the self, also has a varied and murky history, but both books focus primarily mostly on making the cross over one's self.)
More importantly, the sign of the cross is a lesson in discipleship. As Andreopoulos, from an Eastern Orthodox perspective, and Ghezzi, from a Roman Catholic perspective, both show, making sign of the cross is a powerful act of daily prayer, dedication, and remembrance. Ghezzi writes that at its heart, the sign of the cross is "a simple gesture and … a simple prayer."
Over time, Christians have imbued this small, simple gesture with volumes of theological meaning. Holding three fingers together—thumb, forefinger, and middle finger—as you make the sign symbolizes the Trinity. Holding the other two fingers against your palm represents the two natures of Christ, human and divine. Dropping the hand from forehead to waist to begin the gesture represents Christ's descent to earth. The upward movement that follows represents his resurrection. And so on.
Andreopoulos and Ghezzi find in the sign of the cross a symbol of baptism, protection, profession of faith, defiance of the Devil, invocation of God's power, solidarity with the church, and a rebuke of self-indulgence—to name a few.
The origins of the sign are unknown; as Andreopoulos points out: "our information is sparse because this ancient practice emerged naturally, as something that made sense to most Christians." The earliest descriptions, such as Tertullian's, indicate that the cross was made with one finger—probably the thumb—on the forehead in the shape of a Hebrew T or a Greek X, letters that stood for names of God and Christ. Presumably, early Christians were taking their cues from passages in Genesis 4:15, Ezekiel 9:4, and Revelation 14:1 and 22:4 that describe a mark on the forehead as a sign of God's claim on a person.
The similarities among the shapes of T, X, and the cross were noted by early writers, but it wasn't until the fourth century that the cross became a symbol of pride, of worship, and of Christian identity. By then, Augustine declared, "What else is the sign of Christ but the cross of Christ?" and advised that "the sign be applied … to the foreheads of believers."
At some point, Christians began to make the sign with two fingers rather than one, probably to indicate the two natures of Christ, and later, with three fingers to symbolize the Trinity. This change in fingering may have led to the "large cross"—the sign made over the entire upper body, rather than just the forehead. One explanation is that amid ninth-century debates over the nature of the Trinity, Christians may have wanted to emphasize that they were now using three fingers rather than two, and so they used the larger sign to make it more obvious.